[PATCH] nfsd: fix arithmetic expression overflow in decode_saddr()

[Alexandr Sapozhnkiov <alsp705@gmail.com>]

From: Alexandr Sapozhnikov <alsp705@gmail.com>

The value of an arithmetic expression tmp2 * NSEC_PER_USEC 
is a subject to overflow because its operands are not cast 
to a larger data type before performing arithmetic.
If tmp2 == 17,000,000 then the expression tmp2 * NSEC_PER_USEC
will overflow because expression is of type u32.
If tmp2 > 1,000,000 then tv_nsec will give be greater 
than 1 second.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Alexandr Sapozhnikov <alsp705@gmail.com>
---
 fs/nfsd/nfsxdr.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/nfsd/nfsxdr.c b/fs/nfsd/nfsxdr.c
index 5777f40c7353..df62ed5099de 100644
--- a/fs/nfsd/nfsxdr.c
+++ b/fs/nfsd/nfsxdr.c
@@ -172,6 +172,8 @@ svcxdr_decode_sattr(struct svc_rqst *rqstp, struct xdr_stream *xdr,
 	tmp1 = be32_to_cpup(p++);
 	tmp2 = be32_to_cpup(p++);
 	if (tmp1 != (u32)-1 && tmp2 != (u32)-1) {
+		if (tmp2 > 999999)
+			tmp2 = 999999;
 		iap->ia_valid |= ATTR_ATIME | ATTR_ATIME_SET;
 		iap->ia_atime.tv_sec = tmp1;
 		iap->ia_atime.tv_nsec = tmp2 * NSEC_PER_USEC;
@@ -180,6 +182,8 @@ svcxdr_decode_sattr(struct svc_rqst *rqstp, struct xdr_stream *xdr,
 	tmp1 = be32_to_cpup(p++);
 	tmp2 = be32_to_cpup(p++);
 	if (tmp1 != (u32)-1 && tmp2 != (u32)-1) {
+		if (tmp2 > 1000000)
+			tmp2 = 999999;
 		iap->ia_valid |= ATTR_MTIME | ATTR_MTIME_SET;
 		iap->ia_mtime.tv_sec = tmp1;
 		iap->ia_mtime.tv_nsec = tmp2 * NSEC_PER_USEC;
-- 
2.43.0