queue-6.1/fs-smb-client-fix-out-of-bounds-read-in-cifs_sanitiz.patch

From a9cfbd642e7583c0e01d6b6917ec55816747c080 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Mon, 30 Mar 2026 13:11:27 -0700
Subject: fs/smb/client: fix out-of-bounds read in cifs_sanitize_prepath

From: Fredric Cover <FredTheDude@proton.me>

[ Upstream commit 78ec5bf2f589ec7fd8f169394bfeca541b077317 ]

When cifs_sanitize_prepath is called with an empty string or a string
containing only delimiters (e.g., "/"), the current logic attempts to
check *(cursor2 - 1) before cursor2 has advanced. This results in an
out-of-bounds read.

This patch adds an early exit check after stripping prepended
delimiters. If no path content remains, the function returns NULL.

The bug was identified via manual audit and verified using a
standalone test case compiled with AddressSanitizer, which
triggered a SEGV on affected inputs.

Signed-off-by: Fredric Cover <FredTheDude@proton.me>
Reviewed-by: Henrique Carvalho <[2]henrique.carvalho@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/smb/client/fs_context.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
index 9000299e98cb4..35f2c94aafd14 100644
--- a/fs/smb/client/fs_context.c
+++ b/fs/smb/client/fs_context.c
@@ -454,6 +454,10 @@ char *cifs_sanitize_prepath(char *prepath, gfp_t gfp)
 	while (IS_DELIM(*cursor1))
 		cursor1++;
 
+	/* exit in case of only delimiters */
+	if (!*cursor1)
+		return NULL;
+
 	/* copy the first letter */
 	*cursor2 = *cursor1;
 
-- 
2.53.0