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Date: Sun, 14 Aug 2016 22:37:58 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Vegard Nossum <vegard.nossum@...cle.com>, Theodore Tso <tytso@....edu> Subject: [PATCH 4.6 54/56] ext4: validate s_reserved_gdt_blocks on mount 4.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Theodore Ts'o <tytso@....edu> commit 5b9554dc5bf008ae7f68a52e3d7e76c0920938a2 upstream. If s_reserved_gdt_blocks is extremely large, it's possible for ext4_init_block_bitmap(), which is called when ext4 sets up an uninitialized block bitmap, to corrupt random kernel memory. Add the same checks which e2fsck has --- it must never be larger than blocksize / sizeof(__u32) --- and then add a backup check in ext4_init_block_bitmap() in case the superblock gets modified after the file system is mounted. Reported-by: Vegard Nossum <vegard.nossum@...cle.com> Signed-off-by: Theodore Ts'o <tytso@....edu> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- fs/ext4/balloc.c | 3 +++ fs/ext4/super.c | 7 +++++++ 2 files changed, 10 insertions(+) --- a/fs/ext4/balloc.c +++ b/fs/ext4/balloc.c @@ -208,6 +208,9 @@ static int ext4_init_block_bitmap(struct memset(bh->b_data, 0, sb->s_blocksize); bit_max = ext4_num_base_meta_clusters(sb, block_group); + if ((bit_max >> 3) >= bh->b_size) + return -EFSCORRUPTED; + for (bit = 0; bit < bit_max; bit++) ext4_set_bit(bit, bh->b_data); --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -3415,6 +3415,13 @@ static int ext4_fill_super(struct super_ goto failed_mount; } + if (le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks) > (blocksize / 4)) { + ext4_msg(sb, KERN_ERR, + "Number of reserved GDT blocks insanely large: %d", + le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks)); + goto failed_mount; + } + if (sbi->s_mount_opt & EXT4_MOUNT_DAX) { if (blocksize != PAGE_SIZE) { ext4_msg(sb, KERN_ERR,
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