linux-kernel - [PATCH] cifs: fix memory leak in smb3_fs_context_parse

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Message-Id: <20251118150257.35455-1-ssranevjti@gmail.com>
Date: Tue, 18 Nov 2025 20:32:57 +0530
From: ssrane_b23@...vjti.ac.in
To: sfrench@...ba.org
Cc: pc@...guebit.org,
	ronniesahlberg@...il.com,
	sprasad@...rosoft.com,
	tom@...pey.com,
	bharathsm@...rosoft.com,
	linux-cifs@...r.kernel.org,
	samba-technical@...ts.samba.org,
	linux-kernel@...r.kernel.org,
	skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linux.dev,
	david.hunter.linux@...il.com,
	khalid@...nel.org,
	Shaurya Rane <ssrane_b23@...vjti.ac.in>,
	syzbot+87be6809ed9bf6d718e3@...kaller.appspotmail.com
Subject: [PATCH] cifs: fix memory leak in smb3_fs_context_parse_param error path

From: Shaurya Rane <ssrane_b23@...vjti.ac.in>

Add proper cleanup of ctx->source and fc->source to the
cifs_parse_mount_err error handler. This ensures that memory allocated
for the source strings is correctly freed on all error paths, matching
the cleanup already performed in the success path by
smb3_cleanup_fs_context_contents().
Pointers are also set to NULL after freeing to prevent potential
double-free issues.

This change fixes a memory leak originally detected by syzbot. The
leak occurred when processing Opt_source mount options if an error
happened after ctx->source and fc->source were successfully
allocated but before the function completed.

The specific leak sequence was:
1. ctx->source = smb3_fs_context_fullpath(ctx, '/') allocates memory
2. fc->source = kstrdup(ctx->source, GFP_KERNEL) allocates more memory
3. A subsequent error jumps to cifs_parse_mount_err
4. The old error handler freed passwords but not the source strings,
causing the memory to leak.

This issue was not addressed by commit e8c73eb7db0a ("cifs: client:
fix memory leak in smb3_fs_context_parse_param"), which only fixed
leaks from repeated fsconfig() calls but not this error path.

Reported-by: syzbot+87be6809ed9bf6d718e3@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=87be6809ed9bf6d718e3
Fixes: 24e0a1eff9e2 ("cifs: switch to new mount api")
Signed-off-by: Shaurya Rane <ssrane_b23@...vjti.ac.in>
---
 fs/smb/client/fs_context.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
index 0f894d09157b..975f1fa153fd 100644
--- a/fs/smb/client/fs_context.c
+++ b/fs/smb/client/fs_context.c
@@ -1834,6 +1834,12 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
 	ctx->password = NULL;
 	kfree_sensitive(ctx->password2);
 	ctx->password2 = NULL;
+	kfree(ctx->source);
+	ctx->source = NULL;
+	if (fc) {
+		kfree(fc->source);
+		fc->source = NULL;
+	}
 	return -EINVAL;
 }

-- 
2.34.1