Hi all, This patch is the (apparent) correct way to fix the issues regarding some messages with invalid signatures. My previous patch https://lore.kernel.org/linux-cifs/20220918235442.2981-1-ematsumiya@xxxxxxx/ was wrong because a) it covered up the real issue (*), and b) I could never again "reproduce" the "race" -- I had other patches in place when I tested it, and (thus?) the system memory was not in "pristine" conditions, so it's very likely that there's no race at all. (*) Thanks a lot to Tom Talpey for pointing me to the right direction here. Since it sucks to be wrong twice, I'm sending this one as RFC because I wanted to confirm some things: 1) Can I rely on the fact that status != STATUS_SUCCESS means no variable data in the message? I could only infer from the spec, but not really confirm. 2) (probably only in async cases) When the signature fails, for whatever reason, we don't take any action. This doesn't seem right IMHO, e.g. if the message is spoofed, we show a warning that the signatures doesn't match, but I would expect at least for the operation to stop, or maybe even a complete dis/reconnect. 3) For SMB1, I couldn't really use generic/465 as a real confirmation for this because it says "O_DIRECT is not supported". From reading the code and 'man mount.cifs' I understood that this is supported, so what gives? Worth noting that I don't follow/use/test SMB1 too much. The patch does work for other cases I tried though. I hope someone can address my questions/concerts above, and please let me know if the patch is technically and semantically correct. Patch follows. Enzo -------- When verifying a response's signature, the computation will go through the iov buffer (header + response structs) and the over the page data, to verify any dynamic data appended to the message (usually on an SMB2 READ response). When the response is an error, however, specifically on async reads, the page data is allocated before receiving the expected data. Being "valid" data (from the signature computation POV; non-NULL, >0 pages), it's included in the parsing and generates an invalid signature for the message. Fix this by checking if the status is non-zero, and skip the page data if it is. The issue happens in all protocol versions, and this fix applies to all. This issue can be observed with xfstests generic/465. Signed-off-by: Enzo Matsumiya <ematsumiya@xxxxxxx> --- fs/cifs/cifsencrypt.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/fs/cifs/cifsencrypt.c b/fs/cifs/cifsencrypt.c index 46f5718754f9..e3260bb436b3 100644 --- a/fs/cifs/cifsencrypt.c +++ b/fs/cifs/cifsencrypt.c @@ -32,15 +32,28 @@ int __cifs_calc_signature(struct smb_rqst *rqst, int rc; struct kvec *iov = rqst->rq_iov; int n_vec = rqst->rq_nvec; + bool has_error = false; /* iov[0] is actual data and not the rfc1002 length for SMB2+ */ if (!is_smb1(server)) { + struct smb2_hdr *shdr = (struct smb2_hdr *)iov[0].iov_base; + if (iov[0].iov_len <= 4) return -EIO; + + if (shdr->Status != 0) + has_error = true; + i = 0; } else { + struct smb_hdr *hdr = (struct smb_hdr *)iov[1].iov_base; + if (n_vec < 2 || iov[0].iov_len != 4) return -EIO; + + if (hdr->Status.CifsError != 0) + has_error = true; + i = 1; /* skip rfc1002 length */ } @@ -61,6 +74,9 @@ int __cifs_calc_signature(struct smb_rqst *rqst, } } + if (has_error) + goto out_final; + /* now hash over the rq_pages array */ for (i = 0; i < rqst->rq_npages; i++) { void *kaddr; @@ -81,6 +97,7 @@ int __cifs_calc_signature(struct smb_rqst *rqst, kunmap(rqst->rq_pages[i]); } +out_final: rc = crypto_shash_final(shash, signature); if (rc) cifs_dbg(VFS, "%s: Could not generate hash\n", __func__); -- 2.35.3
