ufs_read_cylinder() copies cg_freeoff from the on-disk cylinder group without checking that the free-fragment bitmap fits in the loaded cylinder group buffers. A crafted image can place cg_freeoff past those buffers so that allocation later indexes ubh->bh[] out of range. UBSAN: array-index-out-of-bounds in fs/ufs/balloc.c:752:15 ubh_scanc() fs/ufs/balloc.c:752 ufs_bitmap_search() fs/ufs/balloc.c ufs_alloccg_block() fs/ufs/balloc.c ufs_alloc_fragments() fs/ufs/balloc.c ufs_new_fragments() fs/ufs/balloc.c Reject the cylinder group unless the full BITS_TO_BYTES(s_fpg) free-fragment bitmap starting at c_freeoff fits in the bytes actually loaded for that cylinder group. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: Xiang Mei (Microsoft) Cc: AutonomousCodeSecurity@microsoft.com Cc: stable@vger.kernel.org Signed-off-by: Cen Zhang (Microsoft Security FORGE Labs) --- fs/ufs/cylinder.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/fs/ufs/cylinder.c b/fs/ufs/cylinder.c index a2813270c303..fec6c9dfb055 100644 --- a/fs/ufs/cylinder.c +++ b/fs/ufs/cylinder.c @@ -33,6 +33,8 @@ static bool ufs_read_cylinder(struct super_block *sb, struct ufs_sb_private_info * uspi; struct ufs_cg_private_info * ucpi; struct ufs_cylinder_group * ucg; + u64 cg_bytes, free_bitmap_bytes; + const char *err; unsigned i, j; UFSD("ENTER, cgno %u, bitmap_nr %u\n", cgno, bitmap_nr); @@ -48,8 +50,10 @@ static bool ufs_read_cylinder(struct super_block *sb, UCPI_UBH(ucpi)->bh[0] = sbi->s_ucg[cgno]; for (i = 1; i < UCPI_UBH(ucpi)->count; i++) { UCPI_UBH(ucpi)->bh[i] = sb_bread(sb, UCPI_UBH(ucpi)->fragment + i); - if (!UCPI_UBH(ucpi)->bh[i]) + if (!UCPI_UBH(ucpi)->bh[i]) { + err = "can't read cylinder group block %u"; goto failed; + } } sbi->s_cgno[bitmap_nr] = cgno; @@ -68,6 +72,16 @@ static bool ufs_read_cylinder(struct super_block *sb, ucpi->c_clustersumoff = fs32_to_cpu(sb, ucg->cg_u.cg_44.cg_clustersumoff); ucpi->c_clusteroff = fs32_to_cpu(sb, ucg->cg_u.cg_44.cg_clusteroff); ucpi->c_nclusterblks = fs32_to_cpu(sb, ucg->cg_u.cg_44.cg_nclusterblks); + + cg_bytes = UCPI_UBH(ucpi)->count * sb->s_blocksize; + free_bitmap_bytes = BITS_TO_BYTES((u64)uspi->s_fpg); + /* The full free bitmap must fit in the loaded CG buffer. */ + if (!free_bitmap_bytes || + (u64)ucpi->c_freeoff + free_bitmap_bytes > cg_bytes) { + err = "cylinder group %u has invalid free bitmap"; + goto failed; + } + UFSD("EXIT\n"); return true; @@ -75,7 +89,7 @@ static bool ufs_read_cylinder(struct super_block *sb, for (j = 1; j < i; j++) brelse(UCPI_UBH(ucpi)->bh[j]); sbi->s_cgno[bitmap_nr] = UFS_CGNO_EMPTY; - ufs_error (sb, "ufs_read_cylinder", "can't read cylinder group block %u", cgno); + ufs_error(sb, "ufs_read_cylinder", err, cgno); return false; } base-commit: 786262be6048deab760f68c8acc2c85607165894 -- 2.55.0