linux-kernel - [PATCH 5.4 182/261] ext4: fix error pointer dereference

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Message-Id: <20200619141658.643736204@linuxfoundation.org>
Date:   Fri, 19 Jun 2020 16:33:13 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jeffle Xu <jefflexu@...ux.alibaba.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        Jan Kara <jack@...e.cz>, Theodore Tso <tytso@....edu>,
        stable@...nel.org
Subject: [PATCH 5.4 182/261] ext4: fix error pointer dereference

From: Jeffle Xu <jefflexu@...ux.alibaba.com>

commit 8418897f1bf87da0cb6936489d57a4320c32c0af upstream.

Don't pass error pointers to brelse().

commit 7159a986b420 ("ext4: fix some error pointer dereferences") has fixed
some cases, fix the remaining one case.

Once ext4_xattr_block_find()->ext4_sb_bread() failed, error pointer is
stored in @bs->bh, which will be passed to brelse() in the cleanup
routine of ext4_xattr_set_handle(). This will then cause a NULL panic
crash in __brelse().

BUG: unable to handle kernel NULL pointer dereference at 000000000000005b
RIP: 0010:__brelse+0x1b/0x50
Call Trace:
 ext4_xattr_set_handle+0x163/0x5d0
 ext4_xattr_set+0x95/0x110
 __vfs_setxattr+0x6b/0x80
 __vfs_setxattr_noperm+0x68/0x1b0
 vfs_setxattr+0xa0/0xb0
 setxattr+0x12c/0x1a0
 path_setxattr+0x8d/0xc0
 __x64_sys_setxattr+0x27/0x30
 do_syscall_64+0x60/0x250
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

In this case, @bs->bh stores '-EIO' actually.

Fixes: fb265c9cb49e ("ext4: add ext4_sb_bread() to disambiguate ENOMEM cases")
Signed-off-by: Jeffle Xu <jefflexu@...ux.alibaba.com>
Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>
Cc: stable@...nel.org # 2.6.19
Reviewed-by: Ritesh Harjani <riteshh@...ux.ibm.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Link: https://lore.kernel.org/r/1587628004-95123-1-git-send-email-jefflexu@linux.alibaba.com
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/ext4/xattr.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1820,8 +1820,11 @@ ext4_xattr_block_find(struct inode *inod
 	if (EXT4_I(inode)->i_file_acl) {
 		/* The inode already has an extended attribute block. */
 		bs->bh = ext4_sb_bread(sb, EXT4_I(inode)->i_file_acl, REQ_PRIO);
-		if (IS_ERR(bs->bh))
-			return PTR_ERR(bs->bh);
+		if (IS_ERR(bs->bh)) {
+			error = PTR_ERR(bs->bh);
+			bs->bh = NULL;
+			return error;
+		}
 		ea_bdebug(bs->bh, "b_count=%d, refcount=%d",
 			atomic_read(&(bs->bh->b_count)),
 			le32_to_cpu(BHDR(bs->bh)->h_refcount));