From a3bf0f28d4ba16e1f35f8c983bb04426b87e2a78 Mon Sep 17 00:00:00 2001 From: Junyoung Jang Date: Mon, 4 May 2026 20:26:49 +0900 Subject: [PATCH] fs/statmount: fix slab out-of-bounds write in statmount_mnt_idmap statmount_mnt_idmap() writes one mapping with seq_printf() and then manually advances seq->count to include the NUL separator. If seq_printf() overflows, seq_set_overflow() sets seq->count to seq->size. The manual seq->count++ changes this to seq->size + 1. seq_has_overflowed() then no longer detects the overflow. The corrupted count returns to statmount_string(), which later executes: seq->buf[seq->count++] = '\0'; This causes a 1-byte NULL out-of-bounds write on the dynamically allocated seq buffer. Fix this by checking for overflow immediately after seq_printf(). Fixes: 37c4a9590e1e ("statmount: allow to retrieve idmappings") Signed-off-by: Junyoung Jang Link: https://patch.msgid.link/20260504112649.1862936-1-graypanda.inzag@gmail.com Signed-off-by: Christian Brauner --- fs/mnt_idmapping.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/mnt_idmapping.c b/fs/mnt_idmapping.c index 6472c4ea3d1e..cb61fbdb52e9 100644 --- a/fs/mnt_idmapping.c +++ b/fs/mnt_idmapping.c @@ -375,6 +375,8 @@ int statmount_mnt_idmap(struct mnt_idmap *idmap, struct seq_file *seq, bool uid_ continue; seq_printf(seq, "%u %u %u", extent->first, lower, extent->count); + if (seq_has_overflowed(seq)) + return -EAGAIN; seq->count++; /* mappings are separated by \0 */ if (seq_has_overflowed(seq))