| Message ID | 433928.1745944651@warthog.procyon.org.uk |
|---|---|
| State | New |
| Headers | show |
| Series | afs, bash: Fix open(O_CREAT) on an extant AFS file in a sticky dir | expand |
David, Thanks for this patch. I believe there is one mistake in afs_have_same_owner(). I've added a bit more background which might be incorporated into a future commit message. I have also asked inline about the safety of the use of id-mapped uids for the ownership checks. On 4/29/2025 12:37 PM, David Howells wrote: > > Bash has a work around in redir_open() that causes open(O_CREAT) of a file > in a sticky directory to be retried without O_CREAT if bash was built with > AFS workarounds configured: > > #if defined (AFS) > if ((fd < 0) && (errno == EACCES)) > { > fd = open (filename, flags & ~O_CREAT, mode); > errno = EACCES; /* restore errno */ > } > > #endif /* AFS */ I think its worth clarifying the purpose of this fallback logic and why it exists. The fallback logic was added to bash 1.14.7 as part of the introduction of support for IBM/Transarc AFS 3.4. It was noted that sometimes EEXIST would be returned from open(filename, flags | O_CREAT) but would succeed if open(filename, flags & ~O_CREAT) was called. There is no evidence that the AFS developers were aware of the problem. I can report that the cause of this behavior is the AFS fileserver's checking for PRSFS_INSERT rights on the directory prior to performing the CreateFile action. If the caller is not permitted to create a directory entry the action fails with EACCES even if the requested filename already exists. The most recent versions of IBM AFS 3.6, OpenAFS, and AuriStorFS fileservers all continue to exhibit this behavior today. This logic predated 30aba6656f61ed44cba445a3c0d38b296fa9e8f5 ("namei: allow restricted O_CREAT of FIFOs and regular files") by decades. As a side effect, when the filesystem is an in-tree or out-of-tree AFS-family filesystem ... > This works around the kernel not being able to validly check the > current_fsuid() against i_uid on the file or the directory because the > uidspaces of the system and of AFS may well be disjoint. The problem lies > with the uid checks in may_create_in_sticky(). > > However, the bash work around is going to be removed: > > https://git.savannah.gnu.org/cgit/bash.git/tree/redir.c?h=bash-5.3-rc1#n733 > > Fix this in the kernel by: > > (1) Provide an ->is_owned_by_me() inode op, similar to ->permission(), > and, if provided, call that to determine if the caller owns the file > instead of checking the i_uid to current_fsuid(). > > (2) Provide a ->have_same_owner() inode op, that, if provided, can be > called to see if an inode has the same owner as the parent on the path > walked. > > For kafs, use the first hook to check to see if the server indicated the > ADMINISTER bit in the access rights returned by the FS.FetchStatus and > suchlike The AFSFetchStatus.CallerAccess field returned for a non-directory object includes the PRSFS_ADMINISTER bit set if the caller is authenticated and the authenticated identity is the AFS ID returned in the AFSFetchStatus.Owner field. > and the second hook to compare the AFS user IDs retrieved by > FS.FetchStatus (which may not fit in a kuid if AuriStor's YFS variant). Perhaps more importantly, the AFS IDs specified in the AFSFetchStatus.Owner field often have no relationship to the local system's uid namespace and might collide with various uid ranges which might be used for id-mapping by container managers. > This can be tested by creating a sticky directory (the user must have a > token to do this) and creating a file in it. Then strace bash doing "echo > foo >>file" and look at whether bash does a single, successful O_CREAT open > on the file or whether that one fails and then bash does one without > O_CREAT that succeeds. > > Reported-by: Etienne Champetier <champetier.etienne@gmail.com> > Signed-off-by: David Howells <dhowells@redhat.com> > cc: Marc Dionne <marc.dionne@auristor.com> > cc: Jeffrey Altman <jaltman@auristor.com> > cc: Chet Ramey <chet.ramey@case.edu> > cc: Alexander Viro <viro@zeniv.linux.org.uk> > cc: Christian Brauner <brauner@kernel.org> > cc: Steve French <sfrench@samba.org> > cc: linux-afs@lists.infradead.org > cc: openafs-devel@openafs.org > cc: linux-cifs@vger.kernel.org > cc: linux-fsdevel@vger.kernel.org > --- > fs/afs/dir.c | 2 ++ > fs/afs/file.c | 2 ++ > fs/afs/internal.h | 3 +++ > fs/afs/security.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++ > fs/namei.c | 22 ++++++++++++++++++---- > include/linux/fs.h | 3 +++ > 6 files changed, 80 insertions(+), 4 deletions(-) > > diff --git a/fs/afs/dir.c b/fs/afs/dir.c > index 9e7b1fe82c27..6360db1673b0 100644 > --- a/fs/afs/dir.c > +++ b/fs/afs/dir.c > @@ -65,6 +65,8 @@ const struct inode_operations afs_dir_inode_operations = { > .permission = afs_permission, > .getattr = afs_getattr, > .setattr = afs_setattr, > + .is_owned_by_me = afs_is_owned_by_me, > + .have_same_owner = afs_have_same_owner, > }; > > const struct address_space_operations afs_dir_aops = { > diff --git a/fs/afs/file.c b/fs/afs/file.c > index fc15497608c6..0317f0a36cf2 100644 > --- a/fs/afs/file.c > +++ b/fs/afs/file.c > @@ -47,6 +47,8 @@ const struct inode_operations afs_file_inode_operations = { > .getattr = afs_getattr, > .setattr = afs_setattr, > .permission = afs_permission, > + .is_owned_by_me = afs_is_owned_by_me, > + .have_same_owner = afs_have_same_owner, > }; > > const struct address_space_operations afs_file_aops = { > diff --git a/fs/afs/internal.h b/fs/afs/internal.h > index 440b0e731093..fbfbf615abe3 100644 > --- a/fs/afs/internal.h > +++ b/fs/afs/internal.h > @@ -1495,6 +1495,9 @@ extern struct key *afs_request_key(struct afs_cell *); > extern struct key *afs_request_key_rcu(struct afs_cell *); > extern int afs_check_permit(struct afs_vnode *, struct key *, afs_access_t *); > extern int afs_permission(struct mnt_idmap *, struct inode *, int); > +int afs_is_owned_by_me(struct mnt_idmap *idmap, struct inode *inode); > +int afs_have_same_owner(struct mnt_idmap *idmap, struct inode *inode, > + struct dentry *dentry); > extern void __exit afs_clean_up_permit_cache(void); > > /* > diff --git a/fs/afs/security.c b/fs/afs/security.c > index 6a7744c9e2a2..cc9689fbed47 100644 > --- a/fs/afs/security.c > +++ b/fs/afs/security.c > @@ -477,6 +477,58 @@ int afs_permission(struct mnt_idmap *idmap, struct inode *inode, > return ret; > } > > +/* > + * Determine if an inode is owned by 'me' - whatever that means for the > + * filesystem. In the case of AFS, this means that the file is owned by the > + * AFS user represented by the token (e.g. from a kerberos server) held in a > + * key. Returns 0 if owned by me, 1 if not; can also return an error. > + */ > +int afs_is_owned_by_me(struct mnt_idmap *idmap, struct inode *inode) > +{ > + struct afs_vnode *vnode = AFS_FS_I(inode); > + afs_access_t access; > + struct key *key; > + int ret; > + > + key = afs_request_key(vnode->volume->cell); > + if (IS_ERR(key)) > + return PTR_ERR(key); > + > + /* Get the access rights for the key on this file. */ > + ret = afs_check_permit(vnode, key, &access); > + if (ret < 0) > + goto error; > + > + /* We get the ADMINISTER bit if we own the file. */ > + ret = (access & AFS_ACE_ADMINISTER) ? 0 : 1; > +error: > + key_put(key); > + return ret; > +} > + > +/* > + * Determine if a file has the same owner as its parent - whatever that means > + * for the filesystem. In the case of AFS, this means comparing their AFS > + * UIDs. Returns 0 if same, 1 if not same; can also return an error. > + */ > +int afs_have_same_owner(struct mnt_idmap *idmap, struct inode *inode, > + struct dentry *dentry) > +{ > + struct afs_vnode *vnode = AFS_FS_I(inode); > + struct dentry *parent; > + s64 owner; > + > + /* Get the owner's ID for the directory. Ideally, we'd use RCU to > + * access the parent rather than getting a ref. > + */ > + parent = dget_parent(dentry); > + vnode = AFS_FS_I(d_backing_inode(parent)); This line is overwriting 'vnode' with the parent. I think there needs to be a separate pvnode or something. > + owner = vnode->status.owner; > + dput(parent); > + > + return vnode->status.owner != owner; > +} > + > void __exit afs_clean_up_permit_cache(void) > { > int i; > diff --git a/fs/namei.c b/fs/namei.c > index 84a0e0b0111c..79e8ef1b6900 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -1318,11 +1318,25 @@ static int may_create_in_sticky(struct mnt_idmap *idmap, struct nameidata *nd, > > i_vfsuid = i_uid_into_vfsuid(idmap, inode); Unrelated to this change but is use of id-mapped uid values safe for this purpose? Isn't it possible for more than one uid to be mapped to the same vfsuid value?= > - if (vfsuid_eq(i_vfsuid, dir_vfsuid)) > - return 0; > + if (unlikely(inode->i_op->have_same_owner)) { > + int ret = inode->i_op->have_same_owner(idmap, inode, nd->path.dentry); > > - if (vfsuid_eq_kuid(i_vfsuid, current_fsuid())) > - return 0; > + if (ret <= 0) > + return ret; > + } else { > + if (vfsuid_eq(i_vfsuid, dir_vfsuid)) > + return 0; > + } > + > + if (unlikely(inode->i_op->is_owned_by_me)) { > + int ret = inode->i_op->is_owned_by_me(idmap, inode); > + > + if (ret <= 0) > + return ret; > + } else { > + if (vfsuid_eq_kuid(i_vfsuid, current_fsuid())) > + return 0; > + } > > if (likely(dir_mode & 0002)) { > audit_log_path_denied(AUDIT_ANOM_CREAT, "sticky_create"); > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 016b0fe1536e..ec278d2d362a 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -2236,6 +2236,9 @@ struct inode_operations { > struct dentry *dentry, struct fileattr *fa); > int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa); > struct offset_ctx *(*get_offset_ctx)(struct inode *inode); > + int (*is_owned_by_me)(struct mnt_idmap *idmap, struct inode *inode); > + int (*have_same_owner)(struct mnt_idmap *idmap, struct inode *inode, > + struct dentry *dentry); > } ____cacheline_aligned; > > static inline int call_mmap(struct file *file, struct vm_area_struct *vma) Jeffrey Altman
On 4/29/25 1:35 PM, Jeffrey E Altman wrote: > I think its worth clarifying the purpose of this fallback logic and why it > exists. The fallback > logic was added to bash 1.14.7 as part of the introduction of support for > IBM/Transarc AFS 3.4. The chronology is wrong. The workaround came in in January, 1992, when bash-1.11 was current and IBM released AFS 3.1. (The bug was actually encountered with bash-1.08.) The old code, without the workaround, caused widespread mail delivery failures at CMU, who reported the problem to me and (they claimed at the time) IBM, and provided the patch. > It was noted that sometimes EEXIST would be returned from open(filename, > flags | O_CREAT) > but would succeed if open(filename, flags & ~O_CREAT) was called. There is > no evidence that > the AFS developers were aware of the problem. Well, except for CMU's report.
Chet Ramey <chet.ramey@case.edu> wrote:
> Well, except for CMU's report.
Do you know of any link for that? I'm guessing that is it was 1992, there may
be no online record of it.
David
On 4/30/2025 12:14 PM, David Howells wrote: > Chet Ramey <chet.ramey@case.edu> wrote: > >> Well, except for CMU's report. > Do you know of any link for that? I'm guessing that is it was 1992, there may > be no online record of it. > > David https://groups.google.com/g/gnu.bash.bug/c/6PPTfOgFdL4/m/2AQU-S1N76UJ?hl=en
On 4/30/25 1:26 PM, Jeffrey E Altman wrote: > On 4/30/2025 12:14 PM, David Howells wrote: >> Chet Ramey <chet.ramey@case.edu> wrote: >> >>> Well, except for CMU's report. >> Do you know of any link for that? I'm guessing that is it was 1992, >> there may >> be no online record of it. >> >> David > > https://groups.google.com/g/gnu.bash.bug/c/6PPTfOgFdL4/m/2AQU-S1N76UJ?hl=en Which of course just claims they reported it, but doesn't include the report itself. But Jeffrey's message seems to indicate that IBM addressed this particular issue in AFS 3.2.
On Tue, Apr 29, 2025 at 05:37:31PM +0100, David Howells wrote: > > Bash has a work around in redir_open() that causes open(O_CREAT) of a file > in a sticky directory to be retried without O_CREAT if bash was built with > AFS workarounds configured: > > #if defined (AFS) > if ((fd < 0) && (errno == EACCES)) > { > fd = open (filename, flags & ~O_CREAT, mode); > errno = EACCES; /* restore errno */ > } > > #endif /* AFS */ > > This works around the kernel not being able to validly check the > current_fsuid() against i_uid on the file or the directory because the > uidspaces of the system and of AFS may well be disjoint. The problem lies > with the uid checks in may_create_in_sticky(). > > However, the bash work around is going to be removed: Why is it removed? That's a very strange comment: #if 0 /* reportedly no longer needed */ So then just don't remove it. I don't see a reason for us to workaround userspace creating a bug for itself and forcing us to add two new inode operations to work around it.
On 5/5/2025 10:02 AM, Etienne Champetier wrote: > Hello, > > Removing lists, feel free to add them back > > Le lun. 5 mai 2025 à 09:14, Christian Brauner <brauner@kernel.org> a écrit : >> Why is it removed? That's a very strange comment: >> >> #if 0 /* reportedly no longer needed */ >> >> So then just don't remove it. I don't see a reason for us to workaround >> userspace creating a bug for itself and forcing us to add two new inode >> operations to work around it. > This bash workaround introduced ages ago for AFS bypass fs.protected_regular Chet, I don't think this history is correct. The bash workaround was introduced in 1992 to workaround a behavior when appending to restricted access directories stored in IBM AFS 3.1[1] and the Linux kernel's 30aba6656f61ed44cba445a3c0d38b296fa9e8f5 wasn't added until 2018. IBM AFS 3.2 addressed the narrow use case described by the bug report by implementing a potentially racy change to the AFS cache manager and failing to address the server side. However, that is out of scope for this discussion. To the extent that there is a bug in one or more of the AFS server implementations it should be fixed there. The bash fallback logic to retry the open without O_CREAT introduces a bypass for the kernel mode protection provided by 30aba6656f61 and should be removed. Christian, It just so happens that the workaround added to bash in 1992 masks an incompatibility introduced by 30aba6656f61 when the backing filesystem is "afs" because the ownership checks required by may_create_in_sticky() cannot be reliably performed based upon the kernel's local knowledge of the uids. Ownership checks in "afs" are performed by the fileserver's evaluation of the caller's rxgk or rxkad security tokens and not by use of uids. This incompatibility was only noticed after Red Hat began enabling fs.protected_regular by default and bash removed the fallback logic in the proposed 5.3 release candidates. The proposed inode operations are to permit filesystems such as AFS which cannot rely upon the kernel's local uid knowledge to perform the required the ownership checks to perform those checks via another mechanism. In the case of AFS, the fileserver already conveys the answer to the "is inode owned by me?" question as part of its delivery of caller access rights (AFSFetchStatus.CallerAccess). The answer to the "do these two inodes have the same owner?" question can be determined via comparison of the AFSFetchStatus.Owner fields for each inode which belong to a uid namespace that is specific the the AFS cell in which the inodes are stored. When performing this ownership check for network filesystems I do not believe it is safe to assume that the uid namespace of the network filesystem is identical to the local machine's uid namespace. I think it would be safer for all network filesystems to answer the ownership questions using network uid values instead of local uid values when available. I'm also concerned about using id-mapped values for this comparison because there is no restriction preventing two distinct id values from being mapped to the same id. Sincerely, Jeffrey Altman [1] https://groups.google.com/g/gnu.bash.bug/c/6PPTfOgFdL4/m/2AQU-S1N76UJ
Christian Brauner <brauner@kernel.org> wrote: > > However, the bash work around is going to be removed: > > Why is it removed? That's a very strange comment: Because it makes bash output redirection work differently to other programs, I would guess. It's actually a simple security check to work around (just retry the open() with O_CREAT dropped) - however, it does expose an... error, I suppose, in the Linux kernel: namely that the VFS itself is treating foreign files as if they had local system ownership. We have the ->permission() inode op for this reason (I presume) - but that only applies to certain checks. The VFS must not assume that it can interpret i_uid and i_gid on an inode and must not assume that it can compare them to current->fsuid and current->fs_gid. Now, in my patch, I added two inode ops because they VFS code involved makes two distinct evaluations and so I made an op for each and, as such, those evaluations may be applicable elsewhere, but I could make a combined op that handles that specific situation instead. David
On Tue, May 06, 2025 at 11:26:30AM +0100, David Howells wrote: > Christian Brauner <brauner@kernel.org> wrote: > > > > However, the bash work around is going to be removed: > > > > Why is it removed? That's a very strange comment: > > Because it makes bash output redirection work differently to other programs, I > would guess. It's actually a simple security check to work around (just retry > the open() with O_CREAT dropped) - however, it does expose an... error, I > suppose, in the Linux kernel: namely that the VFS itself is treating foreign > files as if they had local system ownership. > > We have the ->permission() inode op for this reason (I presume) - but that > only applies to certain checks. The VFS must not assume that it can interpret > i_uid and i_gid on an inode and must not assume that it can compare them to > current->fsuid and current->fs_gid. > > Now, in my patch, I added two inode ops because they VFS code involved makes > two distinct evaluations and so I made an op for each and, as such, those > evaluations may be applicable elsewhere, but I could make a combined op that > handles that specific situation instead. Try to make it one, please.
On 5/5/25 9:14 AM, Christian Brauner wrote: >> This works around the kernel not being able to validly check the >> current_fsuid() against i_uid on the file or the directory because the >> uidspaces of the system and of AFS may well be disjoint. The problem lies >> with the uid checks in may_create_in_sticky(). >> >> However, the bash work around is going to be removed: > > Why is it removed? That's a very strange comment: I think this question has been adequately answered. > So then just don't remove it. I don't see a reason for us to workaround > userspace creating a bug for itself and forcing us to add two new inode > operations to work around it. I think this shows that userspace applications should be very cautious about putting in workarounds for kernel bugs, and making them as limited in scope as possible.
On 5/5/25 10:42 AM, Jeffrey E Altman wrote: >>> So then just don't remove it. I don't see a reason for us to workaround >>> userspace creating a bug for itself and forcing us to add two new inode >>> operations to work around it. >> This bash workaround introduced ages ago for AFS bypass fs.protected_regular > > Chet, I don't think this history is correct. I think Etienne's terse comment accurately summarizes the current problem (and maybe it would read more clearly if he had used `bypasses').
diff --git a/fs/afs/dir.c b/fs/afs/dir.c index 9e7b1fe82c27..6360db1673b0 100644 --- a/fs/afs/dir.c +++ b/fs/afs/dir.c @@ -65,6 +65,8 @@ const struct inode_operations afs_dir_inode_operations = { .permission = afs_permission, .getattr = afs_getattr, .setattr = afs_setattr, + .is_owned_by_me = afs_is_owned_by_me, + .have_same_owner = afs_have_same_owner, }; const struct address_space_operations afs_dir_aops = { diff --git a/fs/afs/file.c b/fs/afs/file.c index fc15497608c6..0317f0a36cf2 100644 --- a/fs/afs/file.c +++ b/fs/afs/file.c @@ -47,6 +47,8 @@ const struct inode_operations afs_file_inode_operations = { .getattr = afs_getattr, .setattr = afs_setattr, .permission = afs_permission, + .is_owned_by_me = afs_is_owned_by_me, + .have_same_owner = afs_have_same_owner, }; const struct address_space_operations afs_file_aops = { diff --git a/fs/afs/internal.h b/fs/afs/internal.h index 440b0e731093..fbfbf615abe3 100644 --- a/fs/afs/internal.h +++ b/fs/afs/internal.h @@ -1495,6 +1495,9 @@ extern struct key *afs_request_key(struct afs_cell *); extern struct key *afs_request_key_rcu(struct afs_cell *); extern int afs_check_permit(struct afs_vnode *, struct key *, afs_access_t *); extern int afs_permission(struct mnt_idmap *, struct inode *, int); +int afs_is_owned_by_me(struct mnt_idmap *idmap, struct inode *inode); +int afs_have_same_owner(struct mnt_idmap *idmap, struct inode *inode, + struct dentry *dentry); extern void __exit afs_clean_up_permit_cache(void); /* diff --git a/fs/afs/security.c b/fs/afs/security.c index 6a7744c9e2a2..cc9689fbed47 100644 --- a/fs/afs/security.c +++ b/fs/afs/security.c @@ -477,6 +477,58 @@ int afs_permission(struct mnt_idmap *idmap, struct inode *inode, return ret; } +/* + * Determine if an inode is owned by 'me' - whatever that means for the + * filesystem. In the case of AFS, this means that the file is owned by the + * AFS user represented by the token (e.g. from a kerberos server) held in a + * key. Returns 0 if owned by me, 1 if not; can also return an error. + */ +int afs_is_owned_by_me(struct mnt_idmap *idmap, struct inode *inode) +{ + struct afs_vnode *vnode = AFS_FS_I(inode); + afs_access_t access; + struct key *key; + int ret; + + key = afs_request_key(vnode->volume->cell); + if (IS_ERR(key)) + return PTR_ERR(key); + + /* Get the access rights for the key on this file. */ + ret = afs_check_permit(vnode, key, &access); + if (ret < 0) + goto error; + + /* We get the ADMINISTER bit if we own the file. */ + ret = (access & AFS_ACE_ADMINISTER) ? 0 : 1; +error: + key_put(key); + return ret; +} + +/* + * Determine if a file has the same owner as its parent - whatever that means + * for the filesystem. In the case of AFS, this means comparing their AFS + * UIDs. Returns 0 if same, 1 if not same; can also return an error. + */ +int afs_have_same_owner(struct mnt_idmap *idmap, struct inode *inode, + struct dentry *dentry) +{ + struct afs_vnode *vnode = AFS_FS_I(inode); + struct dentry *parent; + s64 owner; + + /* Get the owner's ID for the directory. Ideally, we'd use RCU to + * access the parent rather than getting a ref. + */ + parent = dget_parent(dentry); + vnode = AFS_FS_I(d_backing_inode(parent)); + owner = vnode->status.owner; + dput(parent); + + return vnode->status.owner != owner; +} + void __exit afs_clean_up_permit_cache(void) { int i; diff --git a/fs/namei.c b/fs/namei.c index 84a0e0b0111c..79e8ef1b6900 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1318,11 +1318,25 @@ static int may_create_in_sticky(struct mnt_idmap *idmap, struct nameidata *nd, i_vfsuid = i_uid_into_vfsuid(idmap, inode); - if (vfsuid_eq(i_vfsuid, dir_vfsuid)) - return 0; + if (unlikely(inode->i_op->have_same_owner)) { + int ret = inode->i_op->have_same_owner(idmap, inode, nd->path.dentry); - if (vfsuid_eq_kuid(i_vfsuid, current_fsuid())) - return 0; + if (ret <= 0) + return ret; + } else { + if (vfsuid_eq(i_vfsuid, dir_vfsuid)) + return 0; + } + + if (unlikely(inode->i_op->is_owned_by_me)) { + int ret = inode->i_op->is_owned_by_me(idmap, inode); + + if (ret <= 0) + return ret; + } else { + if (vfsuid_eq_kuid(i_vfsuid, current_fsuid())) + return 0; + } if (likely(dir_mode & 0002)) { audit_log_path_denied(AUDIT_ANOM_CREAT, "sticky_create"); diff --git a/include/linux/fs.h b/include/linux/fs.h index 016b0fe1536e..ec278d2d362a 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2236,6 +2236,9 @@ struct inode_operations { struct dentry *dentry, struct fileattr *fa); int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa); struct offset_ctx *(*get_offset_ctx)(struct inode *inode); + int (*is_owned_by_me)(struct mnt_idmap *idmap, struct inode *inode); + int (*have_same_owner)(struct mnt_idmap *idmap, struct inode *inode, + struct dentry *dentry); } ____cacheline_aligned; static inline int call_mmap(struct file *file, struct vm_area_struct *vma)
Bash has a work around in redir_open() that causes open(O_CREAT) of a file in a sticky directory to be retried without O_CREAT if bash was built with AFS workarounds configured: #if defined (AFS) if ((fd < 0) && (errno == EACCES)) { fd = open (filename, flags & ~O_CREAT, mode); errno = EACCES; /* restore errno */ } #endif /* AFS */ This works around the kernel not being able to validly check the current_fsuid() against i_uid on the file or the directory because the uidspaces of the system and of AFS may well be disjoint. The problem lies with the uid checks in may_create_in_sticky(). However, the bash work around is going to be removed: https://git.savannah.gnu.org/cgit/bash.git/tree/redir.c?h=bash-5.3-rc1#n733 Fix this in the kernel by: (1) Provide an ->is_owned_by_me() inode op, similar to ->permission(), and, if provided, call that to determine if the caller owns the file instead of checking the i_uid to current_fsuid(). (2) Provide a ->have_same_owner() inode op, that, if provided, can be called to see if an inode has the same owner as the parent on the path walked. For kafs, use the first hook to check to see if the server indicated the ADMINISTER bit in the access rights returned by the FS.FetchStatus and suchlike and the second hook to compare the AFS user IDs retrieved by FS.FetchStatus (which may not fit in a kuid if AuriStor's YFS variant). This can be tested by creating a sticky directory (the user must have a token to do this) and creating a file in it. Then strace bash doing "echo foo >>file" and look at whether bash does a single, successful O_CREAT open on the file or whether that one fails and then bash does one without O_CREAT that succeeds. Reported-by: Etienne Champetier <champetier.etienne@gmail.com> Signed-off-by: David Howells <dhowells@redhat.com> cc: Marc Dionne <marc.dionne@auristor.com> cc: Jeffrey Altman <jaltman@auristor.com> cc: Chet Ramey <chet.ramey@case.edu> cc: Alexander Viro <viro@zeniv.linux.org.uk> cc: Christian Brauner <brauner@kernel.org> cc: Steve French <sfrench@samba.org> cc: linux-afs@lists.infradead.org cc: openafs-devel@openafs.org cc: linux-cifs@vger.kernel.org cc: linux-fsdevel@vger.kernel.org --- fs/afs/dir.c | 2 ++ fs/afs/file.c | 2 ++ fs/afs/internal.h | 3 +++ fs/afs/security.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++ fs/namei.c | 22 ++++++++++++++++++---- include/linux/fs.h | 3 +++ 6 files changed, 80 insertions(+), 4 deletions(-)