NFSv4: Fix possible 1-byte stack overflow in nfs_idmap_read_and_verify_message
In nfs_idmap_read_and_verify_message there is an incorrect sprintf '%d'
that converts the __u32 'im_id' from struct idmap_msg to 'id_str', which
is a stack char array variable of length NFS_UINT_MAXLEN == 11.
If a uid or gid value is >
2147483647 = 0x7fffffff, the conversion
overflows into a negative value, for example:
crash> p (unsigned) (0x80000000)
$1 =
2147483648
crash> p (signed) (0x80000000)
$2 = -
2147483648
The '-' sign is written to the buffer and this causes a 1 byte overflow
when the NULL byte is written, which corrupts kernel stack memory. If
CONFIG_CC_STACKPROTECTOR_STRONG is set we see a stack-protector panic:
[
11558053.616565] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in:
ffffffffa05b8a8c
[
11558053.639063] CPU: 6 PID: 9423 Comm: rpc.idmapd Tainted: G W ------------ T 3.10.0-514.el7.x86_64 #1
[
11558053.641990] Hardware name: Red Hat OpenStack Compute, BIOS 1.10.2-3.el7_4.1 04/01/2014
[
11558053.644462]
ffffffff818c7bc0 00000000b1f3aec1 ffff880de0f9bd48 ffffffff81685eac
[
11558053.646430]
ffff880de0f9bdc8 ffffffff8167f2b3 ffffffff00000010 ffff880de0f9bdd8
[
11558053.648313]
ffff880de0f9bd78 00000000b1f3aec1 ffffffff811dcb03 ffffffffa05b8a8c
[
11558053.650107] Call Trace:
[
11558053.651347] [<
ffffffff81685eac>] dump_stack+0x19/0x1b
[
11558053.653013] [<
ffffffff8167f2b3>] panic+0xe3/0x1f2
[
11558053.666240] [<
ffffffff811dcb03>] ? kfree+0x103/0x140
[
11558053.682589] [<
ffffffffa05b8a8c>] ? idmap_pipe_downcall+0x1cc/0x1e0 [nfsv4]
[
11558053.689710] [<
ffffffff810855db>] __stack_chk_fail+0x1b/0x30
[
11558053.691619] [<
ffffffffa05b8a8c>] idmap_pipe_downcall+0x1cc/0x1e0 [nfsv4]
[
11558053.693867] [<
ffffffffa00209d6>] rpc_pipe_write+0x56/0x70 [sunrpc]
[
11558053.695763] [<
ffffffff811fe12d>] vfs_write+0xbd/0x1e0
[
11558053.702236] [<
ffffffff810acccc>] ? task_work_run+0xac/0xe0
[
11558053.704215] [<
ffffffff811fec4f>] SyS_write+0x7f/0xe0
[
11558053.709674] [<
ffffffff816964c9>] system_call_fastpath+0x16/0x1b
Fix this by calling the internally defined nfs_map_numeric_to_string()
function which properly uses '%u' to convert this __u32. For consistency,
also replace the one other place where snprintf is called.
Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Reported-by: Stephen Johnston <sjohnsto@redhat.com>
Fixes:
cf4ab538f1516 ("NFSv4: Fix the string length returned by the idmapper")
Cc: stable@vger.kernel.org # v3.4+
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>