From: ZhengYuan Huang Date: Wed, 1 Apr 2026 02:16:22 +0000 (+0800) Subject: ocfs2: validate bg_list extent bounds in discontig groups X-Git-Tag: v7.1-rc1~126^2~14 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=6110d18e208cc5572158928401246d98cd2b90b4;p=thirdparty%2Fkernel%2Flinux.git ocfs2: validate bg_list extent bounds in discontig groups [BUG] Running ocfs2 on a corrupted image with a discontiguous block group whose bg_list.l_next_free_rec is set to an excessively large value triggers a KASAN use-after-free crash: BUG: KASAN: use-after-free in ocfs2_bg_discontig_fix_by_rec fs/ocfs2/suballoc.c:1678 [inline] BUG: KASAN: use-after-free in ocfs2_bg_discontig_fix_result+0x4a4/0x560 fs/ocfs2/suballoc.c:1715 Read of size 4 at addr ffff88801a85f000 by task syz.0.115/552 Call Trace: ... __asan_report_load4_noabort+0x14/0x30 mm/kasan/report_generic.c:380 ocfs2_bg_discontig_fix_by_rec fs/ocfs2/suballoc.c:1678 [inline] ocfs2_bg_discontig_fix_result+0x4a4/0x560 fs/ocfs2/suballoc.c:1715 ocfs2_search_one_group fs/ocfs2/suballoc.c:1752 [inline] ocfs2_claim_suballoc_bits+0x13c3/0x1cd0 fs/ocfs2/suballoc.c:1984 ocfs2_claim_new_inode+0x2e7/0x8a0 fs/ocfs2/suballoc.c:2292 ocfs2_mknod_locked.constprop.0+0x121/0x2a0 fs/ocfs2/namei.c:637 ocfs2_mknod+0xc71/0x2400 fs/ocfs2/namei.c:384 ocfs2_create+0x158/0x390 fs/ocfs2/namei.c:676 lookup_open.isra.0+0x10a1/0x1460 fs/namei.c:3796 open_last_lookups fs/namei.c:3895 [inline] path_openat+0x11fe/0x2ce0 fs/namei.c:4131 do_filp_open+0x1f6/0x430 fs/namei.c:4161 do_sys_openat2+0x117/0x1c0 fs/open.c:1437 do_sys_open fs/open.c:1452 [inline] __do_sys_openat fs/open.c:1468 [inline] ... [CAUSE] ocfs2_bg_discontig_fix_result() iterates over bg->bg_list.l_recs[] using l_next_free_rec as the upper bound without any sanity check: for (i = 0; i < le16_to_cpu(bg->bg_list.l_next_free_rec); i++) { rec = &bg->bg_list.l_recs[i]; l_next_free_rec is read directly from the on-disk group descriptor and is trusted blindly. On a 4 KiB block device, bg_list.l_recs[] can hold at most 235 entries (ocfs2_extent_recs_per_gd(sb)). A corrupted or crafted filesystem image can set l_next_free_rec to an arbitrarily large value, causing the loop to index past the end of the group descriptor buffer_head data page and into an adjacent freed page. [FIX] Validate discontiguous bg_list.l_count against ocfs2_extent_recs_per_gd(sb), then reject l_next_free_rec values that exceed l_count. This keeps the on-disk extent list self-consistent and matches how the rest of ocfs2 uses l_count as the extent-list bound. Link: https://lkml.kernel.org/r/20260401021622.3560952-1-gality369@gmail.com Signed-off-by: ZhengYuan Huang Reviewed-by: Joseph Qi Cc: Mark Fasheh Cc: Joel Becker Cc: Junxiao Bi Cc: Changwei Ge Cc: Jun Piao Cc: Heming Zhao Signed-off-by: Andrew Morton --- diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c index bb98bd51338ee..d284e0e372525 100644 --- a/fs/ocfs2/suballoc.c +++ b/fs/ocfs2/suballoc.c @@ -197,6 +197,31 @@ static int ocfs2_validate_gd_self(struct super_block *sb, 8 * le16_to_cpu(gd->bg_size)); } + /* + * For discontiguous block groups, validate the on-disk extent list + * against the maximum number of extent records that can physically + * fit in a single block. + */ + if (ocfs2_gd_is_discontig(gd)) { + u16 max_recs = ocfs2_extent_recs_per_gd(sb); + u16 l_count = le16_to_cpu(gd->bg_list.l_count); + u16 l_next_free_rec = le16_to_cpu(gd->bg_list.l_next_free_rec); + + if (l_count != max_recs) { + do_error("Group descriptor #%llu bad discontig l_count %u expected %u\n", + (unsigned long long)bh->b_blocknr, + l_count, + max_recs); + } + + if (l_next_free_rec > l_count) { + do_error("Group descriptor #%llu bad discontig l_next_free_rec %u max %u\n", + (unsigned long long)bh->b_blocknr, + l_next_free_rec, + l_count); + } + } + return 0; }