| Message ID | 1356727817-10649-1-git-send-email-dborkman@redhat.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Daniel Borkmann <dborkman@redhat.com> Date: Fri, 28 Dec 2012 21:50:17 +0100 > Currently, we return -EINVAL for malformed or wrong BPF filters. > However, this is not done for BPF_S_ANC* operations, which makes it > more difficult to detect if it's actually supported or not by the > BPF machine. Therefore, we should also return -EINVAL if K is within > the SKF_AD_OFF universe and the ancillary operation did not match. ... > Cc: Eric Dumazet <eric.dumazet@gmail.com> > Reported-by: Ani Sinha <ani@aristanetworks.com> > Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Applied, thanks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/core/filter.c b/net/core/filter.c index c23543c..2ead2a9 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -532,6 +532,7 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen) [BPF_JMP|BPF_JSET|BPF_X] = BPF_S_JMP_JSET_X, }; int pc; + bool anc_found; if (flen == 0 || flen > BPF_MAXINSNS) return -EINVAL; @@ -592,8 +593,10 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen) case BPF_S_LD_W_ABS: case BPF_S_LD_H_ABS: case BPF_S_LD_B_ABS: + anc_found = false; #define ANCILLARY(CODE) case SKF_AD_OFF + SKF_AD_##CODE: \ code = BPF_S_ANC_##CODE; \ + anc_found = true; \ break switch (ftest->k) { ANCILLARY(PROTOCOL); @@ -610,6 +613,10 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen) ANCILLARY(VLAN_TAG); ANCILLARY(VLAN_TAG_PRESENT); } + + /* ancillary operation unknown or unsupported */ + if (anc_found == false && ftest->k >= SKF_AD_OFF) + return -EINVAL; } ftest->code = code; }
Currently, we return -EINVAL for malformed or wrong BPF filters. However, this is not done for BPF_S_ANC* operations, which makes it more difficult to detect if it's actually supported or not by the BPF machine. Therefore, we should also return -EINVAL if K is within the SKF_AD_OFF universe and the ancillary operation did not match. Why exactly is it needed? If tools such as libpcap/tcpdump want to make use of new ancillary operations (like filtering VLAN in kernel space), there is currently no sane way to test if this feature / BPF_S_ANC* op is present or not, since no error is returned. This patch will make life easier for that and allow for a proper usage for user space applications. There was concern, if this patch will break userland. Short answer: Yes and no. Long answer: It will "break" only for code that calls ... { BPF_LD | BPF_(W|H|B) | BPF_ABS, 0, 0, <K> }, ... where <K> is in [0xfffff000, 0xffffffff] _and_ <K> is *not* an ancillary. And here comes the BUT: assuming some *old* code will have such an instruction where <K> is between [0xfffff000, 0xffffffff] and it doesn't know ancillary operations, then this will give a non-expected / unwanted behavior as well (since we do not return the BPF machine with 0 after a failed load_pointer(), which was the case before introducing ancillary operations, but load sth. into the accumulator instead, and continue with the next instruction, for instance). Thus, user space code would already have been broken by introducing ancillary operations into the BPF machine per se. Code that does such a direct load, e.g. "load word at packet offset 0xffffffff into accumulator" ("ld [0xffffffff]") is quite broken, isn't it? The whole assumption of ancillary operations is that no-one intentionally calls things like "ld [0xffffffff]" and expect this word to be loaded from such a packet offset. Hence, we can also safely make use of this feature testing patch and facilitate application development. Therefore, at least from this patch onwards, we have *for sure* a check whether current or in future implemented BPF_S_ANC* ops are supported in the kernel. Patch was tested on x86_64. (Thanks to Eric for the previous review.) Cc: Eric Dumazet <eric.dumazet@gmail.com> Reported-by: Ani Sinha <ani@aristanetworks.com> Signed-off-by: Daniel Borkmann <dborkman@redhat.com> --- net/core/filter.c | 7 +++++++ 1 file changed, 7 insertions(+)