From 6513a81e9325d712f1bfb9a1d7b750134e49ff18 Mon Sep 17 00:00:00 2001 From: Suresh Jayaraman Date: Wed, 31 Mar 2010 12:00:03 +0530 Subject: cifs: Fix a kernel BUG with remote OS/2 server (try #3) 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: Stable Reviewed-by: Jeff Layton Signed-off-by: Suresh Jayaraman Signed-off-by: Steve French --- fs/cifs/cifssmb.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'fs/cifs/cifssmb.c') diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c index e1f90a3a016..f213b8ae43c 100644 --- a/fs/cifs/cifssmb.c +++ b/fs/cifs/cifssmb.c @@ -1518,6 +1518,14 @@ 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); @@ -1606,6 +1614,14 @@ 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 */ -- cgit v1.2.3-70-g09d2