On Tue, 2018-04-17 at 16:11 -0400, Dave Wysochanski wrote: > In nfs_idmap_read_and_verify_message there is an unprotected sprintf > that converts the __u32 'im_id' from struct idmap_msg to 'id_str' > that is a stack variable of 'NFS_UINT_MAXLEN' (defined as 11). > If a uid or gid value is > 2147483647 = 0x7fffffff we corrupt > kernel memory by one byte and if CONFIG_CC_STACKPROTECTOR_STRONG > is set we see a stack-protector panic as follows: > > [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 snprintf and a safe length based on sizeof(id_str). > > Signed-off-by: Dave Wysochanski <dwysocha@xxxxxxxxxx> > Reported-by: Stephen Johnston <sjohnsto@xxxxxxxxxx> > --- > fs/nfs/nfs4idmap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/nfs/nfs4idmap.c b/fs/nfs/nfs4idmap.c > index 22dc30a679a0..a8c663f8dd99 100644 > --- a/fs/nfs/nfs4idmap.c > +++ b/fs/nfs/nfs4idmap.c > @@ -627,7 +627,7 @@ static int nfs_idmap_read_and_verify_message(struct idmap_msg *im, > if (strcmp(upcall->im_name, im->im_name) != 0) > break; > /* Note: here we store the NUL terminator too */ > - len = sprintf(id_str, "%d", im->im_id) + 1; > + len = snprintf(id_str, sizeof(id_str), "%u", im->im_id) + 1; > ret = nfs_idmap_instantiate(key, authkey, id_str, len); > break; > case IDMAP_CONV_IDTONAME: I did not see any reply to this and we did have one customer hit this which caused a considerable outage of many machines. In essence once this happened, it became a DoS on all machines using idmapping and they implemented a temporary workaround. Anna / Trond - if you need me to improve the patch header or want clarification or see a problem with it, please let me know. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
