From patchwork Wed Mar 31 06:30:03 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: cifs: Fix a kernel BUG with remote OS/2 server (try #3) Date: Tue, 30 Mar 2010 20:30:03 -0000 From: Suresh Jayaraman X-Patchwork-Id: 49081 Message-Id: <1270017003-7523-1-git-send-email-sjayaraman@suse.de> To: Steve French Cc: Jeff Layton , linux-cifs-client@lists.samba.org (Please consider for -stable once reviewed and accepted). While chasing a bug report involving a OS/2 server, I noticed the server sets pSMBr->CountHigh to a incorrect value even in case of normal writes. This results in 'nbytes' being computed wrongly and triggers a kernel BUG at mm/filemap.c. void iov_iter_advance(struct iov_iter *i, size_t bytes) { BUG_ON(i->count < bytes); <--- BUG here Why the server is setting 'CountHigh' is not clear but only does so after writing 64k bytes. Though this looks like the server bug, the client side crash may not be acceptable. The workaround is to mask off high 16 bits if the number of bytes written as returned by the server is greater than the bytes requested by the client as suggested by Jeff Layton. Cc: Jeff Layton Signed-off-by: Suresh Jayaraman Reviewed-by: Jeff Layton --- fs/cifs/cifssmb.c | 16 ++++++++++++++++ 1 files changed, 16 insertions(+), 0 deletions(-) diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c index 7cc7f83..7d8ada8 100644 --- a/fs/cifs/cifssmb.c +++ b/fs/cifs/cifssmb.c @@ -1517,6 +1517,14 @@ CIFSSMBWrite(const int xid, struct cifsTconInfo *tcon, *nbytes = le16_to_cpu(pSMBr->CountHigh); *nbytes = (*nbytes) << 16; *nbytes += le16_to_cpu(pSMBr->Count); + + /* + * Mask off high 16 bits when bytes written as returned by the + * server is greater than bytes requested by the client. Some + * OS/2 servers are known to set incorrect CountHigh values. + */ + if (*nbytes > count) + *nbytes &= 0xFFFF; } cifs_buf_release(pSMB); @@ -1605,6 +1613,14 @@ CIFSSMBWrite2(const int xid, struct cifsTconInfo *tcon, *nbytes = le16_to_cpu(pSMBr->CountHigh); *nbytes = (*nbytes) << 16; *nbytes += le16_to_cpu(pSMBr->Count); + + /* + * Mask off high 16 bits when bytes written as returned by the + * server is greater than bytes requested by the client. OS/2 + * servers are known to set incorrect CountHigh values. + */ + if (*nbytes > count) + *nbytes &= 0xFFFF; } /* cifs_small_buf_release(pSMB); */ /* Freed earlier now in SendReceive2 */