| Message ID | 20190107200224.220467-1-sdf@google.com |
|---|---|
| State | Changes Requested |
| Delegated to: | David Miller |
| Headers | show |
| Series | [net,1/2] tun: hold napi_mutex for all napi operations | expand |
On Mon, Jan 7, 2019 at 12:02 PM Stanislav Fomichev <sdf@google.com> wrote: > > BUG: unable to handle kernel NULL pointer dereference at 00000000000000d1 > Call Trace: > ? napi_gro_frags+0xa7/0x2c0 > tun_get_user+0xb50/0xf20 > tun_chr_write_iter+0x53/0x70 > new_sync_write+0xff/0x160 > vfs_write+0x191/0x1e0 > __x64_sys_write+0x5e/0xd0 > do_syscall_64+0x47/0xf0 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > I think there is a subtle race between sending a packet via tap and > attaching it: > > CPU0: CPU1: > tun_chr_ioctl(TUNSETIFF) > tun_set_iff > tun_attach > rcu_assign_pointer(tfile->tun, tun); > tun_fops->write_iter() > tun_chr_write_iter > tun_napi_alloc_frags > napi_get_frags > napi->skb = napi_alloc_skb > tun_napi_init > netif_napi_add > napi->skb = NULL > napi->skb is NULL here > napi_gro_frags > napi_frags_skb > skb = napi->skb > skb_reset_mac_header(skb) > panic() > > To fix, do the following: > * Move rcu_assign_pointer(tfile->tun, tun) to be the last thing we do > in tun_attach(); this should guarantee that when we call tun_get() > we always get an initialized object > * As another safeguard, always grab napi_mutex whenever doing any > napi operation; this should prevent napi state change between > calls to napi_get_frags and napi_gro_frags > > Reported-by: syzbot <syzkaller@googlegroups.com> > Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver") > > Signed-off-by: Stanislav Fomichev <sdf@google.com> > --- > drivers/net/tun.c | 18 +++++++++++++++--- > 1 file changed, 15 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index a4fdad475594..7875f06011f2 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -323,22 +323,30 @@ static void tun_napi_init(struct tun_struct *tun, struct tun_file *tfile, > tfile->napi_enabled = napi_en; > tfile->napi_frags_enabled = napi_en && napi_frags; > if (napi_en) { > + mutex_lock(&tfile->napi_mutex); > netif_napi_add(tun->dev, &tfile->napi, tun_napi_poll, > NAPI_POLL_WEIGHT); > napi_enable(&tfile->napi); > + mutex_unlock(&tfile->napi_mutex); > } > } > > static void tun_napi_disable(struct tun_file *tfile) > { > - if (tfile->napi_enabled) > + if (tfile->napi_enabled) { > + mutex_lock(&tfile->napi_mutex); > napi_disable(&tfile->napi); > + mutex_unlock(&tfile->napi_mutex); > + } > } > > static void tun_napi_del(struct tun_file *tfile) > { > - if (tfile->napi_enabled) > + if (tfile->napi_enabled) { > + mutex_lock(&tfile->napi_mutex); > netif_napi_del(&tfile->napi); > + mutex_unlock(&tfile->napi_mutex); > + } > } > > static bool tun_napi_frags_enabled(const struct tun_file *tfile) > @@ -856,7 +864,6 @@ static int tun_attach(struct tun_struct *tun, struct file *file, > err = 0; > } > > - rcu_assign_pointer(tfile->tun, tun); > rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile); > tun->numqueues++; > > @@ -876,6 +883,11 @@ static int tun_attach(struct tun_struct *tun, struct file *file, > * refcnt. > */ > > + /* All tun_fops depend on tun_get() returning non-null pointer. > + * Thus, assigning tun to a tfile should be the last init operation, > + * otherwise we risk using half-initialized object. > + */ > + rcu_assign_pointer(tfile->tun, tun); > out: > return err; > } Hmmm I believe the issue is different : We need to call tun_napi_init() before doing the publish in the tun->tfiles[] array My patch was : diff --git a/drivers/net/tun.c b/drivers/net/tun.c index a4fdad47559462fbd049a89f880cc3fb33d1151d..dc751d1cbc21a2e2687c5739b44322cd64d0cb46 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -857,15 +857,15 @@ static int tun_attach(struct tun_struct *tun, struct file *file, } rcu_assign_pointer(tfile->tun, tun); + if (!tfile->detached) { + tun_napi_init(tun, tfile, napi, napi_frags); + sock_hold(&tfile->sk); + } rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile); tun->numqueues++; - if (tfile->detached) { + if (tfile->detached) tun_enable_queue(tfile); - } else { - sock_hold(&tfile->sk); - tun_napi_init(tun, tfile, napi, napi_frags); - } if (rtnl_dereference(tun->xdp_prog)) sock_set_flag(&tfile->sk, SOCK_XDP);
On 01/07, Eric Dumazet wrote: > On Mon, Jan 7, 2019 at 12:02 PM Stanislav Fomichev <sdf@google.com> wrote: > > > > BUG: unable to handle kernel NULL pointer dereference at 00000000000000d1 > > Call Trace: > > ? napi_gro_frags+0xa7/0x2c0 > > tun_get_user+0xb50/0xf20 > > tun_chr_write_iter+0x53/0x70 > > new_sync_write+0xff/0x160 > > vfs_write+0x191/0x1e0 > > __x64_sys_write+0x5e/0xd0 > > do_syscall_64+0x47/0xf0 > > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > I think there is a subtle race between sending a packet via tap and > > attaching it: > > > > CPU0: CPU1: > > tun_chr_ioctl(TUNSETIFF) > > tun_set_iff > > tun_attach > > rcu_assign_pointer(tfile->tun, tun); > > tun_fops->write_iter() > > tun_chr_write_iter > > tun_napi_alloc_frags > > napi_get_frags > > napi->skb = napi_alloc_skb > > tun_napi_init > > netif_napi_add > > napi->skb = NULL > > napi->skb is NULL here > > napi_gro_frags > > napi_frags_skb > > skb = napi->skb > > skb_reset_mac_header(skb) > > panic() > > > > To fix, do the following: > > * Move rcu_assign_pointer(tfile->tun, tun) to be the last thing we do > > in tun_attach(); this should guarantee that when we call tun_get() > > we always get an initialized object > > * As another safeguard, always grab napi_mutex whenever doing any > > napi operation; this should prevent napi state change between > > calls to napi_get_frags and napi_gro_frags > > > > Reported-by: syzbot <syzkaller@googlegroups.com> > > Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver") > > > > Signed-off-by: Stanislav Fomichev <sdf@google.com> > > --- > > drivers/net/tun.c | 18 +++++++++++++++--- > > 1 file changed, 15 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > > index a4fdad475594..7875f06011f2 100644 > > --- a/drivers/net/tun.c > > +++ b/drivers/net/tun.c > > @@ -323,22 +323,30 @@ static void tun_napi_init(struct tun_struct *tun, struct tun_file *tfile, > > tfile->napi_enabled = napi_en; > > tfile->napi_frags_enabled = napi_en && napi_frags; > > if (napi_en) { > > + mutex_lock(&tfile->napi_mutex); > > netif_napi_add(tun->dev, &tfile->napi, tun_napi_poll, > > NAPI_POLL_WEIGHT); > > napi_enable(&tfile->napi); > > + mutex_unlock(&tfile->napi_mutex); > > } > > } > > > > static void tun_napi_disable(struct tun_file *tfile) > > { > > - if (tfile->napi_enabled) > > + if (tfile->napi_enabled) { > > + mutex_lock(&tfile->napi_mutex); > > napi_disable(&tfile->napi); > > + mutex_unlock(&tfile->napi_mutex); > > + } > > } > > > > static void tun_napi_del(struct tun_file *tfile) > > { > > - if (tfile->napi_enabled) > > + if (tfile->napi_enabled) { > > + mutex_lock(&tfile->napi_mutex); > > netif_napi_del(&tfile->napi); > > + mutex_unlock(&tfile->napi_mutex); > > + } > > } > > > > static bool tun_napi_frags_enabled(const struct tun_file *tfile) > > @@ -856,7 +864,6 @@ static int tun_attach(struct tun_struct *tun, struct file *file, > > err = 0; > > } > > > > - rcu_assign_pointer(tfile->tun, tun); > > rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile); > > tun->numqueues++; > > > > @@ -876,6 +883,11 @@ static int tun_attach(struct tun_struct *tun, struct file *file, > > * refcnt. > > */ > > > > + /* All tun_fops depend on tun_get() returning non-null pointer. > > + * Thus, assigning tun to a tfile should be the last init operation, > > + * otherwise we risk using half-initialized object. > > + */ > > + rcu_assign_pointer(tfile->tun, tun); > > out: > > return err; > > } > > Hmmm I believe the issue is different : We need to call > tun_napi_init() before doing the publish in the tun->tfiles[] array > > My patch was : Still fails with your patch. Maybe the best way is to move both of those publishes (tfile->tun and tun->tfiles[]) to the end of tun_attach? It looks like tfile->tun is a publish for syscall side (most of tun_socket_ops and tun_fops call tun_get which looks at tun->dev and bail out if it's NULL) and tun->tfiles is (mostly, but not really) for napi side. Here is a repro I'm using if you want to poke it: syz-execprog -threaded -collide -repeat=0 -procs=6 <rep.syz> # See https://goo.gl/kgGztJ for information about syzkaller reproducers. #{"threaded":true,"collide":true,"repeat":true,"procs":6,"sandbox":"none","fault_call":-1,"tun":true,"tmpdir":true,"cgroups":true,"netdev":true,"resetnet":true,"segv":true} openat$tun(0xffffffffffffff9c, 0x0, 0x0, 0x0) r0 = openat$tun(0xffffffffffffff9c, &(0x7f0000001a00)='/dev/net/tun\x00', 0x0, 0x0) ioctl$TUNSETIFF(r0, 0x400454ca, &(0x7f0000000300)={"6e72300100", 0x1132}) r1 = socket$kcm(0x2, 0x3, 0x2) ioctl$PERF_EVENT_IOC_SET_FILTER(r1, 0x8914, &(0x7f0000000780)="6e7230010060a19ef9d2c673d9a1571cb9e1369bcd61ef7e49793ae18712eceb1daa769497800b7fbbd35b170c10751d39aeb660d863e49b8c4f3b3dad48902b5b2d6cfd0abd372c63bcf5d70df3fd4d2e8d443c88bc0e5637dd82fc3435bed4de5d693c9a781c863e05d8a6f8689a5be29216061f3ff53f8b6b396678e7ba155ef9152d7e43b1eccb2331eb8eb1ed5586dcf8b3b0b999361a44ff2c22c2abbef42dd24eabe6723346a6e46c0499a21442d8d00dcb57f013ff7595edd0ff076930de3675d34117a44eb0e4f832936da44e57e43a3e36bd48d2a85bf4fd4a804e83f2f3cf378a435af5e287d4e27337b4ada11b26219832ec6b2b38446b3b95fe3771e9f42ca30fb21e12f0a3d8bc2d85454af9fcc0232d8fd909448b01f46c593d31ea1c926465e35a4199079c3ca41128b17cb01fbf5b522be0fd02022ada37fecc14b6c8c8831883b85a1106f2f867020d529f17a350f20dd3bf51a98cfda70c2e3638a483fd3f87940bb478b07c4c110394c0093d17955089f2ca97bbe075124c9b1ff6500d536a95d96f03d48596e008bf0a028b539cec796cec9bf585eb80fe3e0d26") perf_event_open$cgroup(&(0x7f0000000440)={0x7, 0x70, 0x1, 0x0, 0x6e36, 0x38000000, 0x0, 0x1, 0x21060, 0x0, 0x0, 0x0, 0x20, 0x3, 0xfc50, 0x9, 0x8000, 0x0, 0x0, 0x0, 0x46c8, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x8, 0x3f, 0x401, 0x8001, 0x8, 0x9, 0x0, 0x0, 0x1, 0x1, @perf_config_ext={0x100000000, 0x6}, 0x10, 0x5, 0x2, 0x7, 0xfffffffffffffff9, 0x0, 0x7}, 0xffffffffffffffff, 0x5, 0xffffffffffffffff, 0x0) # 0x2 = O_RDWR r2 = openat$tun(0xffffffffffffff9c, &(0x7f0000001a00)='/dev/net/tun\x00', 0x2, 0x0) # IFF_TAP 0x0002 # IFF_NAPI 0x0010 # IFF_NAPI_FRAGS 0x0020 # IFF_MULTI_QUEUE 0x0100 # IFF_MULTICAST = 0x1000 ioctl$TUNSETIFF(r2, 0x400454ca, &(0x7f0000000300)={"6e72300100", 0x1132}) write$cgroup_int(r2, &(0x7f0000000000), 0x17b) > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index a4fdad47559462fbd049a89f880cc3fb33d1151d..dc751d1cbc21a2e2687c5739b44322cd64d0cb46 > 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -857,15 +857,15 @@ static int tun_attach(struct tun_struct *tun, > struct file *file, > } > > rcu_assign_pointer(tfile->tun, tun); > + if (!tfile->detached) { > + tun_napi_init(tun, tfile, napi, napi_frags); > + sock_hold(&tfile->sk); > + } > rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile); > tun->numqueues++; > > - if (tfile->detached) { > + if (tfile->detached) > tun_enable_queue(tfile); > - } else { > - sock_hold(&tfile->sk); > - tun_napi_init(tun, tfile, napi, napi_frags); > - } > > if (rtnl_dereference(tun->xdp_prog)) > sock_set_flag(&tfile->sk, SOCK_XDP);
On 01/07/2019 01:02 PM, Stanislav Fomichev wrote: > On 01/07, Eric Dumazet wrote: >> On Mon, Jan 7, 2019 at 12:02 PM Stanislav Fomichev <sdf@google.com> wrote: >>> >>> BUG: unable to handle kernel NULL pointer dereference at 00000000000000d1 >>> Call Trace: >>> ? napi_gro_frags+0xa7/0x2c0 >>> tun_get_user+0xb50/0xf20 >>> tun_chr_write_iter+0x53/0x70 >>> new_sync_write+0xff/0x160 >>> vfs_write+0x191/0x1e0 >>> __x64_sys_write+0x5e/0xd0 >>> do_syscall_64+0x47/0xf0 >>> entry_SYSCALL_64_after_hwframe+0x44/0xa9 >>> >>> I think there is a subtle race between sending a packet via tap and >>> attaching it: >>> >>> CPU0: CPU1: >>> tun_chr_ioctl(TUNSETIFF) >>> tun_set_iff >>> tun_attach >>> rcu_assign_pointer(tfile->tun, tun); >>> tun_fops->write_iter() >>> tun_chr_write_iter >>> tun_napi_alloc_frags >>> napi_get_frags >>> napi->skb = napi_alloc_skb >>> tun_napi_init >>> netif_napi_add >>> napi->skb = NULL >>> napi->skb is NULL here >>> napi_gro_frags >>> napi_frags_skb >>> skb = napi->skb >>> skb_reset_mac_header(skb) >>> panic() >>> >>> To fix, do the following: >>> * Move rcu_assign_pointer(tfile->tun, tun) to be the last thing we do >>> in tun_attach(); this should guarantee that when we call tun_get() >>> we always get an initialized object >>> * As another safeguard, always grab napi_mutex whenever doing any >>> napi operation; this should prevent napi state change between >>> calls to napi_get_frags and napi_gro_frags >>> >>> Reported-by: syzbot <syzkaller@googlegroups.com> >>> Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver") >>> >>> Signed-off-by: Stanislav Fomichev <sdf@google.com> >>> --- >>> drivers/net/tun.c | 18 +++++++++++++++--- >>> 1 file changed, 15 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c >>> index a4fdad475594..7875f06011f2 100644 >>> --- a/drivers/net/tun.c >>> +++ b/drivers/net/tun.c >>> @@ -323,22 +323,30 @@ static void tun_napi_init(struct tun_struct *tun, struct tun_file *tfile, >>> tfile->napi_enabled = napi_en; >>> tfile->napi_frags_enabled = napi_en && napi_frags; >>> if (napi_en) { >>> + mutex_lock(&tfile->napi_mutex); >>> netif_napi_add(tun->dev, &tfile->napi, tun_napi_poll, >>> NAPI_POLL_WEIGHT); >>> napi_enable(&tfile->napi); >>> + mutex_unlock(&tfile->napi_mutex); >>> } >>> } >>> >>> static void tun_napi_disable(struct tun_file *tfile) >>> { >>> - if (tfile->napi_enabled) >>> + if (tfile->napi_enabled) { >>> + mutex_lock(&tfile->napi_mutex); >>> napi_disable(&tfile->napi); >>> + mutex_unlock(&tfile->napi_mutex); >>> + } >>> } >>> >>> static void tun_napi_del(struct tun_file *tfile) >>> { >>> - if (tfile->napi_enabled) >>> + if (tfile->napi_enabled) { >>> + mutex_lock(&tfile->napi_mutex); >>> netif_napi_del(&tfile->napi); >>> + mutex_unlock(&tfile->napi_mutex); >>> + } >>> } >>> >>> static bool tun_napi_frags_enabled(const struct tun_file *tfile) >>> @@ -856,7 +864,6 @@ static int tun_attach(struct tun_struct *tun, struct file *file, >>> err = 0; >>> } >>> >>> - rcu_assign_pointer(tfile->tun, tun); >>> rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile); >>> tun->numqueues++; >>> >>> @@ -876,6 +883,11 @@ static int tun_attach(struct tun_struct *tun, struct file *file, >>> * refcnt. >>> */ >>> >>> + /* All tun_fops depend on tun_get() returning non-null pointer. >>> + * Thus, assigning tun to a tfile should be the last init operation, >>> + * otherwise we risk using half-initialized object. >>> + */ >>> + rcu_assign_pointer(tfile->tun, tun); >>> out: >>> return err; >>> } >> >> Hmmm I believe the issue is different : We need to call >> tun_napi_init() before doing the publish in the tun->tfiles[] array >> >> My patch was : > Still fails with your patch. > > Maybe the best way is to move both of those publishes (tfile->tun and > tun->tfiles[]) to the end of tun_attach? It looks like tfile->tun > is a publish for syscall side (most of tun_socket_ops and tun_fops call > tun_get which looks at tun->dev and bail out if it's NULL) and tun->tfiles > is (mostly, but not really) for napi side. > > Here is a repro I'm using if you want to poke it: > > syz-execprog -threaded -collide -repeat=0 -procs=6 <rep.syz> > > # See https://goo.gl/kgGztJ for information about syzkaller reproducers. > #{"threaded":true,"collide":true,"repeat":true,"procs":6,"sandbox":"none","fault_call":-1,"tun":true,"tmpdir":true,"cgroups":true,"netdev":true,"resetnet":true,"segv":true} > openat$tun(0xffffffffffffff9c, 0x0, 0x0, 0x0) > r0 = openat$tun(0xffffffffffffff9c, > &(0x7f0000001a00)='/dev/net/tun\x00', 0x0, 0x0) > ioctl$TUNSETIFF(r0, 0x400454ca, &(0x7f0000000300)={"6e72300100", > 0x1132}) > r1 = socket$kcm(0x2, 0x3, 0x2) > ioctl$PERF_EVENT_IOC_SET_FILTER(r1, 0x8914, > &(0x7f0000000780)="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") > perf_event_open$cgroup(&(0x7f0000000440)={0x7, 0x70, 0x1, 0x0, 0x6e36, > 0x38000000, 0x0, 0x1, 0x21060, 0x0, 0x0, 0x0, 0x20, 0x3, 0xfc50, 0x9, > 0x8000, 0x0, 0x0, 0x0, 0x46c8, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, > 0x0, 0x0, 0x8, 0x3f, 0x401, 0x8001, 0x8, 0x9, 0x0, 0x0, 0x1, 0x1, > @perf_config_ext={0x100000000, 0x6}, 0x10, 0x5, 0x2, 0x7, > 0xfffffffffffffff9, 0x0, 0x7}, 0xffffffffffffffff, 0x5, > 0xffffffffffffffff, 0x0) > # 0x2 = O_RDWR > r2 = openat$tun(0xffffffffffffff9c, > &(0x7f0000001a00)='/dev/net/tun\x00', 0x2, 0x0) > # IFF_TAP 0x0002 > # IFF_NAPI 0x0010 > # IFF_NAPI_FRAGS 0x0020 > # IFF_MULTI_QUEUE 0x0100 > # IFF_MULTICAST = 0x1000 > ioctl$TUNSETIFF(r2, 0x400454ca, &(0x7f0000000300)={"6e72300100", > 0x1132}) > write$cgroup_int(r2, &(0x7f0000000000), 0x17b) > > I dunno, I would prefer to not throw all these mutex_lock(&tfile->napi_mutex)/mutex_unlock(&tfile->napi_mutex) all over the places. Please publish a minimal patches, or a patch series explaining why each fix is needed. I do not really see why tun_napi_disable() and/or tun_napi_del() needs extra synchronization.
On 01/07, Eric Dumazet wrote: > > > On 01/07/2019 01:02 PM, Stanislav Fomichev wrote: > > On 01/07, Eric Dumazet wrote: > >> On Mon, Jan 7, 2019 at 12:02 PM Stanislav Fomichev <sdf@google.com> wrote: > >>> > >>> BUG: unable to handle kernel NULL pointer dereference at 00000000000000d1 > >>> Call Trace: > >>> ? napi_gro_frags+0xa7/0x2c0 > >>> tun_get_user+0xb50/0xf20 > >>> tun_chr_write_iter+0x53/0x70 > >>> new_sync_write+0xff/0x160 > >>> vfs_write+0x191/0x1e0 > >>> __x64_sys_write+0x5e/0xd0 > >>> do_syscall_64+0x47/0xf0 > >>> entry_SYSCALL_64_after_hwframe+0x44/0xa9 > >>> > >>> I think there is a subtle race between sending a packet via tap and > >>> attaching it: > >>> > >>> CPU0: CPU1: > >>> tun_chr_ioctl(TUNSETIFF) > >>> tun_set_iff > >>> tun_attach > >>> rcu_assign_pointer(tfile->tun, tun); > >>> tun_fops->write_iter() > >>> tun_chr_write_iter > >>> tun_napi_alloc_frags > >>> napi_get_frags > >>> napi->skb = napi_alloc_skb > >>> tun_napi_init > >>> netif_napi_add > >>> napi->skb = NULL > >>> napi->skb is NULL here > >>> napi_gro_frags > >>> napi_frags_skb > >>> skb = napi->skb > >>> skb_reset_mac_header(skb) > >>> panic() > >>> > >>> To fix, do the following: > >>> * Move rcu_assign_pointer(tfile->tun, tun) to be the last thing we do > >>> in tun_attach(); this should guarantee that when we call tun_get() > >>> we always get an initialized object > >>> * As another safeguard, always grab napi_mutex whenever doing any > >>> napi operation; this should prevent napi state change between > >>> calls to napi_get_frags and napi_gro_frags > >>> > >>> Reported-by: syzbot <syzkaller@googlegroups.com> > >>> Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver") > >>> > >>> Signed-off-by: Stanislav Fomichev <sdf@google.com> > >>> --- > >>> drivers/net/tun.c | 18 +++++++++++++++--- > >>> 1 file changed, 15 insertions(+), 3 deletions(-) > >>> > >>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c > >>> index a4fdad475594..7875f06011f2 100644 > >>> --- a/drivers/net/tun.c > >>> +++ b/drivers/net/tun.c > >>> @@ -323,22 +323,30 @@ static void tun_napi_init(struct tun_struct *tun, struct tun_file *tfile, > >>> tfile->napi_enabled = napi_en; > >>> tfile->napi_frags_enabled = napi_en && napi_frags; > >>> if (napi_en) { > >>> + mutex_lock(&tfile->napi_mutex); > >>> netif_napi_add(tun->dev, &tfile->napi, tun_napi_poll, > >>> NAPI_POLL_WEIGHT); > >>> napi_enable(&tfile->napi); > >>> + mutex_unlock(&tfile->napi_mutex); > >>> } > >>> } > >>> > >>> static void tun_napi_disable(struct tun_file *tfile) > >>> { > >>> - if (tfile->napi_enabled) > >>> + if (tfile->napi_enabled) { > >>> + mutex_lock(&tfile->napi_mutex); > >>> napi_disable(&tfile->napi); > >>> + mutex_unlock(&tfile->napi_mutex); > >>> + } > >>> } > >>> > >>> static void tun_napi_del(struct tun_file *tfile) > >>> { > >>> - if (tfile->napi_enabled) > >>> + if (tfile->napi_enabled) { > >>> + mutex_lock(&tfile->napi_mutex); > >>> netif_napi_del(&tfile->napi); > >>> + mutex_unlock(&tfile->napi_mutex); > >>> + } > >>> } > >>> > >>> static bool tun_napi_frags_enabled(const struct tun_file *tfile) > >>> @@ -856,7 +864,6 @@ static int tun_attach(struct tun_struct *tun, struct file *file, > >>> err = 0; > >>> } > >>> > >>> - rcu_assign_pointer(tfile->tun, tun); > >>> rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile); > >>> tun->numqueues++; > >>> > >>> @@ -876,6 +883,11 @@ static int tun_attach(struct tun_struct *tun, struct file *file, > >>> * refcnt. > >>> */ > >>> > >>> + /* All tun_fops depend on tun_get() returning non-null pointer. > >>> + * Thus, assigning tun to a tfile should be the last init operation, > >>> + * otherwise we risk using half-initialized object. > >>> + */ > >>> + rcu_assign_pointer(tfile->tun, tun); > >>> out: > >>> return err; > >>> } > >> > >> Hmmm I believe the issue is different : We need to call > >> tun_napi_init() before doing the publish in the tun->tfiles[] array > >> > >> My patch was : > > Still fails with your patch. > > > > Maybe the best way is to move both of those publishes (tfile->tun and > > tun->tfiles[]) to the end of tun_attach? It looks like tfile->tun > > is a publish for syscall side (most of tun_socket_ops and tun_fops call > > tun_get which looks at tun->dev and bail out if it's NULL) and tun->tfiles > > is (mostly, but not really) for napi side. > > > > Here is a repro I'm using if you want to poke it: > > > > syz-execprog -threaded -collide -repeat=0 -procs=6 <rep.syz> > > > > # See https://goo.gl/kgGztJ for information about syzkaller reproducers. > > #{"threaded":true,"collide":true,"repeat":true,"procs":6,"sandbox":"none","fault_call":-1,"tun":true,"tmpdir":true,"cgroups":true,"netdev":true,"resetnet":true,"segv":true} > > openat$tun(0xffffffffffffff9c, 0x0, 0x0, 0x0) > > r0 = openat$tun(0xffffffffffffff9c, > > &(0x7f0000001a00)='/dev/net/tun\x00', 0x0, 0x0) > > ioctl$TUNSETIFF(r0, 0x400454ca, &(0x7f0000000300)={"6e72300100", > > 0x1132}) > > r1 = socket$kcm(0x2, 0x3, 0x2) > > ioctl$PERF_EVENT_IOC_SET_FILTER(r1, 0x8914, > > &(0x7f0000000780)="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") > > perf_event_open$cgroup(&(0x7f0000000440)={0x7, 0x70, 0x1, 0x0, 0x6e36, > > 0x38000000, 0x0, 0x1, 0x21060, 0x0, 0x0, 0x0, 0x20, 0x3, 0xfc50, 0x9, > > 0x8000, 0x0, 0x0, 0x0, 0x46c8, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, > > 0x0, 0x0, 0x8, 0x3f, 0x401, 0x8001, 0x8, 0x9, 0x0, 0x0, 0x1, 0x1, > > @perf_config_ext={0x100000000, 0x6}, 0x10, 0x5, 0x2, 0x7, > > 0xfffffffffffffff9, 0x0, 0x7}, 0xffffffffffffffff, 0x5, > > 0xffffffffffffffff, 0x0) > > # 0x2 = O_RDWR > > r2 = openat$tun(0xffffffffffffff9c, > > &(0x7f0000001a00)='/dev/net/tun\x00', 0x2, 0x0) > > # IFF_TAP 0x0002 > > # IFF_NAPI 0x0010 > > # IFF_NAPI_FRAGS 0x0020 > > # IFF_MULTI_QUEUE 0x0100 > > # IFF_MULTICAST = 0x1000 > > ioctl$TUNSETIFF(r2, 0x400454ca, &(0x7f0000000300)={"6e72300100", > > 0x1132}) > > write$cgroup_int(r2, &(0x7f0000000000), 0x17b) > > > > > > I dunno, I would prefer to not throw all these > mutex_lock(&tfile->napi_mutex)/mutex_unlock(&tfile->napi_mutex) all over the places. > > Please publish a minimal patches, or a patch series explaining why each fix is needed. > > I do not really see why tun_napi_disable() and/or tun_napi_del() needs extra synchronization. They don't, I've added them mostly for consistency. The main issue I was trying to fix (and the one I think I'm hitting) is the one in tun_get_user, where we do the following: 1. mutex_lock(&tfile->napi_mutex); 2. skb = tun_napi_alloc_frags(tfile, copylen, from); * skb = napi_get_frags(&tfile->napi); * napi->skb = napi_alloc_skb() 3. <something happens here that sets napi->skb to NULL> 4. napi_gro_frags(&tfile->napi); * skb = napi_frags_skb(napi); * struct sk_buff *skb = napi->skb; * skb_reset_mac_header(skb); * null pointer deref 5. mutex_unlock(&tfile->napi_mutex); We can basically always grab napi_mutex for all napi-related operations to make sure nothing happens to napi->skb in between napi_get_frags and napi_frags_skb or don't publish tfile->tun so tun_get_user never gets called. I'll send a v2 without napi_mutex'es, I've added them mostly as an additional safeguard. Publishing both tfile->tun and tun->tfiles at the end of tun_attach should be enough.
diff --git a/drivers/net/tun.c b/drivers/net/tun.c index a4fdad475594..7875f06011f2 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -323,22 +323,30 @@ static void tun_napi_init(struct tun_struct *tun, struct tun_file *tfile, tfile->napi_enabled = napi_en; tfile->napi_frags_enabled = napi_en && napi_frags; if (napi_en) { + mutex_lock(&tfile->napi_mutex); netif_napi_add(tun->dev, &tfile->napi, tun_napi_poll, NAPI_POLL_WEIGHT); napi_enable(&tfile->napi); + mutex_unlock(&tfile->napi_mutex); } } static void tun_napi_disable(struct tun_file *tfile) { - if (tfile->napi_enabled) + if (tfile->napi_enabled) { + mutex_lock(&tfile->napi_mutex); napi_disable(&tfile->napi); + mutex_unlock(&tfile->napi_mutex); + } } static void tun_napi_del(struct tun_file *tfile) { - if (tfile->napi_enabled) + if (tfile->napi_enabled) { + mutex_lock(&tfile->napi_mutex); netif_napi_del(&tfile->napi); + mutex_unlock(&tfile->napi_mutex); + } } static bool tun_napi_frags_enabled(const struct tun_file *tfile) @@ -856,7 +864,6 @@ static int tun_attach(struct tun_struct *tun, struct file *file, err = 0; } - rcu_assign_pointer(tfile->tun, tun); rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile); tun->numqueues++; @@ -876,6 +883,11 @@ static int tun_attach(struct tun_struct *tun, struct file *file, * refcnt. */ + /* All tun_fops depend on tun_get() returning non-null pointer. + * Thus, assigning tun to a tfile should be the last init operation, + * otherwise we risk using half-initialized object. + */ + rcu_assign_pointer(tfile->tun, tun); out: return err; }
BUG: unable to handle kernel NULL pointer dereference at 00000000000000d1 Call Trace: ? napi_gro_frags+0xa7/0x2c0 tun_get_user+0xb50/0xf20 tun_chr_write_iter+0x53/0x70 new_sync_write+0xff/0x160 vfs_write+0x191/0x1e0 __x64_sys_write+0x5e/0xd0 do_syscall_64+0x47/0xf0 entry_SYSCALL_64_after_hwframe+0x44/0xa9 I think there is a subtle race between sending a packet via tap and attaching it: CPU0: CPU1: tun_chr_ioctl(TUNSETIFF) tun_set_iff tun_attach rcu_assign_pointer(tfile->tun, tun); tun_fops->write_iter() tun_chr_write_iter tun_napi_alloc_frags napi_get_frags napi->skb = napi_alloc_skb tun_napi_init netif_napi_add napi->skb = NULL napi->skb is NULL here napi_gro_frags napi_frags_skb skb = napi->skb skb_reset_mac_header(skb) panic() To fix, do the following: * Move rcu_assign_pointer(tfile->tun, tun) to be the last thing we do in tun_attach(); this should guarantee that when we call tun_get() we always get an initialized object * As another safeguard, always grab napi_mutex whenever doing any napi operation; this should prevent napi state change between calls to napi_get_frags and napi_gro_frags Reported-by: syzbot <syzkaller@googlegroups.com> Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver") Signed-off-by: Stanislav Fomichev <sdf@google.com> --- drivers/net/tun.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)