From: Michael Bommarito Date: Fri, 15 May 2026 14:23:27 +0000 (-0400) Subject: udf: validate free block extents against the partition length X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5f0419457f89dce1a3f1c8e62a3adf2f39ab8168;p=thirdparty%2Fkernel%2Flinux.git udf: validate free block extents against the partition length udf_free_blocks() checks the logical block number and count against the partition length, but drops the extent offset from that final bound. A crafted extent can pass the guard while logicalBlockNum + offset + count points past the partition, which later indexes past the space bitmap array. A single ftruncate(2) on a file backed by such an extent reliably panics the kernel. This is a local availability issue. On desktop systems where UDisks/polkit allows the active user to mount removable UDF media without CAP_SYS_ADMIN, an unprivileged local user can supply the crafted filesystem and trigger the panic by truncating a writable file on it. Systems that require root or CAP_SYS_ADMIN to mount the image have a higher prerequisite. No confidentiality or integrity impact is claimed: the reproduced primitive is an out-of-bounds read of a bitmap pointer slot followed by a kernel panic. Use the already computed logicalBlockNum + offset + count value for the partition length check. Also make load_block_bitmap() reject an out-of-range block group before indexing s_block_bitmap[], so corrupted callers cannot walk past the flexible array. Fixes: 56e69e59751d ("udf: prevent integer overflow in udf_bitmap_free_blocks()") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-7 Signed-off-by: Michael Bommarito Link: https://patch.msgid.link/20260515142327.1120767-1-michael.bommarito@gmail.com Signed-off-by: Jan Kara --- diff --git a/fs/udf/balloc.c b/fs/udf/balloc.c index 807c493ed0cd5..cc6dc6e1d84de 100644 --- a/fs/udf/balloc.c +++ b/fs/udf/balloc.c @@ -82,8 +82,9 @@ static int load_block_bitmap(struct super_block *sb, int nr_groups = bitmap->s_nr_groups; if (block_group >= nr_groups) { - udf_debug("block_group (%u) > nr_groups (%d)\n", + udf_debug("block_group (%u) >= nr_groups (%d)\n", block_group, nr_groups); + return -EFSCORRUPTED; } if (bitmap->s_block_bitmap[block_group]) { @@ -662,7 +663,7 @@ void udf_free_blocks(struct super_block *sb, struct inode *inode, if (check_add_overflow(bloc->logicalBlockNum, offset, &blk) || check_add_overflow(blk, count, &blk) || - bloc->logicalBlockNum + count > map->s_partition_len) { + blk > map->s_partition_len) { udf_debug("Invalid request to free blocks: (%d, %u), off %u, " "len %u, partition len %u\n", partition, bloc->logicalBlockNum, offset, count,