[PATCH] erofs-utils: lib: fix wrong NULL check after erofs_balloc() in metabox

[Utkal Singh <singhutkal015@gmail.com>]

erofs_balloc() returns an error pointer via ERR_PTR(-errno) on failure,
never NULL. The previous check:

    if (!bh)

fails to detect error pointers since ERR_PTR encodes errors as non-zero
pointers near ULONG_MAX. This causes PTR_ERR(bh) on the next line to be
unreachable, and the subsequent erofs_mapbh() call to receive an invalid
pointer, potentially causing a crash or silent memory corruption.

Replace with the correct IS_ERR() pattern which properly detects all
error pointer values returned by erofs_balloc().

Fixes: 7928074b7643 ("erofs-utils: introduce metadata compression [metabox]")
Signed-off-by: Utkal Singh <utkalsingh059@gmail.com>
---
 lib/metabox.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/metabox.c b/lib/metabox.c
index d6abd51..12706aa 100644
--- a/lib/metabox.c
+++ b/lib/metabox.c
@@ -127,7 +127,7 @@ int erofs_metazone_flush(struct erofs_sb_info *sbi)
 	if (!m2gr)
 		return 0;
 	bh = erofs_balloc(sbi->bmgr, DATA, 0, 0);
-	if (!bh)
+	if (IS_ERR(bh))
 		return PTR_ERR(bh);
 	erofs_mapbh(NULL, bh->block);
 	pos_out = erofs_btell(bh, false);
-- 
2.43.0