From fa236c2b2d4436d9f19ee4e5d5924e90ffd7bb43 Mon Sep 17 00:00:00 2001
From: Arturo Giusti <koredump@protonmail.com>
Date: Tue, 18 May 2021 12:34:57 +0200
Subject: [PATCH] udf: Fix NULL pointer dereference in udf_symlink function
Git-commit: fa236c2b2d4436d9f19ee4e5d5924e90ffd7bb43
Patch-mainline: v5.14-rc1
References: bsc#1206646

In function udf_symlink, epos.bh is assigned with the value returned
by udf_tgetblk. The function udf_tgetblk is defined in udf/misc.c
and returns the value of sb_getblk function that could be NULL.
Then, epos.bh is used without any check, causing a possible
NULL pointer dereference when sb_getblk fails.

This fix adds a check to validate the value of epos.bh.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=213083
Signed-off-by: Arturo Giusti <koredump@protonmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/udf/namei.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/udf/namei.c b/fs/udf/namei.c
index 3ae9f1e91984..7c7c9bbbfa57 100644
--- a/fs/udf/namei.c
+++ b/fs/udf/namei.c
@@ -934,6 +934,10 @@ static int udf_symlink(struct user_namespace *mnt_userns, struct inode *dir,
 				iinfo->i_location.partitionReferenceNum,
 				0);
 		epos.bh = udf_tgetblk(sb, block);
+		if (unlikely(!epos.bh)) {
+			err = -ENOMEM;
+			goto out_no_entry;
+		}
 		lock_buffer(epos.bh);
 		memset(epos.bh->b_data, 0x00, bsize);
 		set_buffer_uptodate(epos.bh);
-- 
2.35.3