[PATCH v2] fs/jfs: fix NULL pointer dereference in metapage_read_folio

[Sridhar Markonda <sridharm@linux.ibm.com>]

This patch fixes a NULL pointer dereference in JFS found during syzkaller
testing on PowerPC systems using large page sizes.

Full crash report:

BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: null-ptr-deref in atomic_inc include/linux/atomic/atomic-instrumented.h:435 [inline]
BUG: KASAN: null-ptr-deref in inc_io fs/jfs/jfs_metapage.c:140 [inline]
BUG: KASAN: null-ptr-deref in metapage_read_folio+0x238/0x7b4 fs/jfs/jfs_metapage.c:587
Write of size 4 at addr 0000000000000004 by task syz.6.4880/59986

CPU: 1 UID: 0 PID: 59986 Comm: syz.6.4880 Tainted: G             L      syzkaller #0 PREEMPT
Tainted: [L]=SOFTLOCKUP
Hardware name: IBM,9105-22A POWER10 (architected) 0x800200 0xf000006 of:IBM,FW1060.51 (NL1060_148) hv:phyp pSeries
Call Trace:
[c00000006e836e30] [c000000000bf948c] print_report mm/kasan/report.c:485 [inline]
[c00000006e836e30] [c000000000bf948c] print_report+0x444/0x9a0 mm/kasan/report.c:471
[c00000006e836f10] [c000000000bf9c10] kasan_report+0x12c/0x218 mm/kasan/report.c:595
[c00000006e837020] [c000000000bfc62c] check_region_inline mm/kasan/generic.c:186 [inline]
[c00000006e837020] [c000000000bfc62c] kasan_check_range+0x270/0x380 mm/kasan/generic.c:200
[c00000006e837060] [c000000000bfd664] __kasan_check_write+0x20/0x34 mm/kasan/shadow.c:37
[c00000006e837080] [c000000001acb808] instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
[c00000006e837080] [c000000001acb808] atomic_inc include/linux/atomic/atomic-instrumented.h:435 [inline]
[c00000006e837080] [c000000001acb808] inc_io fs/jfs/jfs_metapage.c:140 [inline]
[c00000006e837080] [c000000001acb808] metapage_read_folio+0x238/0x7b4 fs/jfs/jfs_metapage.c:587
[c00000006e837130] [c000000000950df0] filemap_read_folio+0xa0/0x268 mm/filemap.c:2501
[c00000006e837180] [c00000000095c234] do_read_cache_folio+0x2d8/0x5c4 mm/filemap.c:4101
[c00000006e837200] [c000000001acd974] read_mapping_folio include/linux/pagemap.h:1028 [inline]
[c00000006e837200] [c000000001acd974] __get_metapage+0x1c4/0xd78 fs/jfs/jfs_metapage.c:729
[c00000006e8372e0] [c000000001a947c8] xtSplitRoot+0xd8/0x874 fs/jfs/jfs_xtree.c:1242
[c00000006e8373d0] [c000000001a97a4c] xtSplitUp+0xad0/0x1240 fs/jfs/jfs_xtree.c:785
[c00000006e837580] [c000000001a98ea0] xtInsert+0x7c0/0xa18 fs/jfs/jfs_xtree.c:608
[c00000006e837780] [c000000001ac851c] extAlloc+0x7bc/0xc74 fs/jfs/jfs_extent.c:150
[c00000006e8378b0] [c000000001a8a7a0] jfs_get_block+0x3c0/0x868 fs/jfs/inode.c:254
[c00000006e837950] [c000000000e1af2c] __block_write_begin_int+0x3c8/0x1318 fs/buffer.c:2142
[c00000006e837a60] [c000000000e1bf98] block_write_begin+0xac/0x230 fs/buffer.c:2253
[c00000006e837ab0] [c000000001a8c454] jfs_write_begin+0x58/0x114 fs/jfs/inode.c:306
[c00000006e837af0] [c000000000949a30] generic_perform_write+0x2e8/0x754 mm/filemap.c:4319
[c00000006e837bf0] [c000000000964174] __generic_file_write_iter+0x210/0x244 mm/filemap.c:4436
[c00000006e837c40] [c0000000009642a4] generic_file_write_iter+0xfc/0x35c mm/filemap.c:4462
[c00000006e837ca0] [c000000000cf9cfc] new_sync_write fs/read_write.c:595 [inline]
[c00000006e837ca0] [c000000000cf9cfc] vfs_write+0x530/0x95c fs/read_write.c:688
[c00000006e837d90] [c000000000cfa4c8] ksys_write+0xf0/0x230 fs/read_write.c:740
[c00000006e837df0] [c00000000004ebbc] system_call_exception+0x26c/0x760 arch/powerpc/kernel/syscall.c:153
[c00000006e837e50] [c00000000000d05c] system_call_vectored_common+0x15c/0x2ec

The crash occurs when insert_metapage() fails to allocate a meta_anchor
structure. The function returns an error code, but its return value was
ignored, leading to a NULL pointer dereference in inc_io().

Check the return value from insert_metapage() and stop processing the
folio when allocation fails.

Fixes: 7fab479bebb9 ("[PATCH] JFS: Support page sizes greater than 4K")

Signed-off-by: Sridhar Markonda <sridharm@linux.ibm.com>
---
Changes in v2:
- Keep insert_metapage() in its original location.
- Check and return errors from insert_metapage().
- Update the Fixes tag.
- Test with xfstests on ppc64le (64K pages); no regressions observed.
---
 fs/jfs/jfs_metapage.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
index 41fe12e641ce..ffbb186e850c 100644
--- a/fs/jfs/jfs_metapage.c
+++ b/fs/jfs/jfs_metapage.c
@@ -573,6 +573,7 @@ static int metapage_read_folio(struct file *fp, struct folio *folio)
 	int xlen;
 	unsigned int len;
 	int offset;
+	int ret = 0;
 
 	BUG_ON(!folio_test_locked(folio));
 	page_start = folio_pos(folio) >> inode->i_blkbits;
@@ -583,8 +584,11 @@ static int metapage_read_folio(struct file *fp, struct folio *folio)
 		pblock = metapage_get_blocks(inode, page_start + block_offset,
 					     &xlen);
 		if (pblock) {
-			if (!folio->private)
-				insert_metapage(folio, NULL);
+			if (!folio->private) {
+				ret = insert_metapage(folio, NULL);
+				if (ret)
+					break;
+			}
 			inc_io(folio);
 			if (bio)
 				submit_bio(bio);
@@ -607,7 +611,7 @@ static int metapage_read_folio(struct file *fp, struct folio *folio)
 	else
 		folio_unlock(folio);
 
-	return 0;
+	return ret;
 }
 
 static bool metapage_release_folio(struct folio *folio, gfp_t gfp_mask)
-- 
2.52.0