udf: Fix NULL pointer dereference in udf_symlink function

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>

diff --git a/fs/udf/namei.c b/fs/udf/namei.c
index 3ae9f1e..7c7c9bb 100644 (file)
--- 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);