[PATCH 4.9 132/245] udf: Fix NULL pointer dereference in udf_symlink function

[Greg Kroah-Hartman]

From: Arturo Giusti <koredump@xxxxxxxxxxxxxx>

[ Upstream commit fa236c2b2d4436d9f19ee4e5d5924e90ffd7bb43 ]

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@xxxxxxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/udf/namei.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/udf/namei.c b/fs/udf/namei.c
index 348b922d1b6a..bfa53dead8c8 100644
--- a/fs/udf/namei.c
+++ b/fs/udf/namei.c
@@ -956,6 +956,10 @@ static int udf_symlink(struct inode *dir, struct dentry *dentry,
 				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);
-- 
2.30.2