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ext4: allow ext4_get_group_info() to fail

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Previously, ext4_get_group_info() would treat an invalid group number
as BUG(), since in theory it should never happen.  However, if a
malicious attaker (or fuzzer) modifies the superblock via the block
device while it is the file system is mounted, it is possible for
s_first_data_block to get set to a very large number.  In that case,
when calculating the block group of some block number (such as the
starting block of a preallocation region), could result in an
underflow and very large block group number.  Then the BUG_ON check in
ext4_get_group_info() would fire, resutling in a denial of service
attack that can be triggered by root or someone with write access to
the block device.

For a quality of implementation perspective, it's best that even if
the system administrator does something that they shouldn't, that it
will not trigger a BUG.  So instead of BUG'ing, ext4_get_group_info()
will call ext4_error and return NULL.  We also add fallback code in
all of the callers of ext4_get_group_info() that it might NULL.

Also, since ext4_get_group_info() was already borderline to be an
inline function, un-inline it.  The results in a next reduction of the
compiled text size of ext4 by roughly 2k.

Cc: stable@kernel.org
Link: https://lore.kernel.org/r/20230430154311.579720-2-tytso@mit.edu
Reported-by: syzbot+e2efa3efc15a1c9e95c3@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=69b28112e098b070f639efb356393af3ffec4220
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Theodore Ts'o 2023-04-29 00:06:28 -04:00
parent 949f95ff39
commit 5354b2af34
5 changed files with 82 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
fs/ext4/balloc.c
View File

@ -321,6 +321,22 @@ static ext4_fsblk_t ext4_valid_block_bitmap_padding(struct super_block *sb,
return (next_zero_bit < bitmap_size ? next_zero_bit : 0);
}
struct ext4_group_info *ext4_get_group_info(struct super_block *sb,
ext4_group_t group)
{
struct ext4_group_info **grp_info;
long indexv, indexh;
if (unlikely(group >= EXT4_SB(sb)->s_groups_count)) {
ext4_error(sb, "invalid group %u", group);
return NULL;
}
indexv = group >> (EXT4_DESC_PER_BLOCK_BITS(sb));
indexh = group & ((EXT4_DESC_PER_BLOCK(sb)) - 1);
grp_info = sbi_array_rcu_deref(EXT4_SB(sb), s_group_info, indexv);
return grp_info[indexh];
}
/*
* Return the block number which was discovered to be invalid, or 0 if
* the block bitmap is valid.
@ -395,7 +411,7 @@ static int ext4_validate_block_bitmap(struct super_block *sb,
if (buffer_verified(bh))
return 0;
if (EXT4_MB_GRP_BBITMAP_CORRUPT(grp))
if (!grp || EXT4_MB_GRP_BBITMAP_CORRUPT(grp))
return -EFSCORRUPTED;
ext4_lock_group(sb, block_group);

15
fs/ext4/ext4.h
View File

@ -2625,6 +2625,8 @@ extern void ext4_check_blocks_bitmap(struct super_block *);
extern struct ext4_group_desc * ext4_get_group_desc(struct super_block * sb,
ext4_group_t block_group,
struct buffer_head ** bh);
extern struct ext4_group_info *ext4_get_group_info(struct super_block *sb,
ext4_group_t group);
extern int ext4_should_retry_alloc(struct super_block *sb, int *retries);
extern struct buffer_head *ext4_read_block_bitmap_nowait(struct super_block *sb,
@ -3232,19 +3234,6 @@ static inline void ext4_isize_set(struct ext4_inode *raw_inode, loff_t i_size)
raw_inode->i_size_high = cpu_to_le32(i_size >> 32);
}
static inline
struct ext4_group_info *ext4_get_group_info(struct super_block *sb,
ext4_group_t group)
{
struct ext4_group_info **grp_info;
long indexv, indexh;
BUG_ON(group >= EXT4_SB(sb)->s_groups_count);
indexv = group >> (EXT4_DESC_PER_BLOCK_BITS(sb));
indexh = group & ((EXT4_DESC_PER_BLOCK(sb)) - 1);
grp_info = sbi_array_rcu_deref(EXT4_SB(sb), s_group_info, indexv);
return grp_info[indexh];
}
/*
* Reading s_groups_count requires using smp_rmb() afterwards. See
* the locking protocol documented in the comments of ext4_group_add()

12
fs/ext4/ialloc.c
View File

@ -91,7 +91,7 @@ static int ext4_validate_inode_bitmap(struct super_block *sb,
if (buffer_verified(bh))
return 0;
if (EXT4_MB_GRP_IBITMAP_CORRUPT(grp))
if (!grp || EXT4_MB_GRP_IBITMAP_CORRUPT(grp))
return -EFSCORRUPTED;
ext4_lock_group(sb, block_group);
@ -293,7 +293,7 @@ void ext4_free_inode(handle_t *handle, struct inode *inode)
}
if (!(sbi->s_mount_state & EXT4_FC_REPLAY)) {
grp = ext4_get_group_info(sb, block_group);
if (unlikely(EXT4_MB_GRP_IBITMAP_CORRUPT(grp))) {
if (!grp || unlikely(EXT4_MB_GRP_IBITMAP_CORRUPT(grp))) {
fatal = -EFSCORRUPTED;
goto error_return;
}
@ -1046,7 +1046,7 @@ got_group:
* Skip groups with already-known suspicious inode
* tables
*/
if (EXT4_MB_GRP_IBITMAP_CORRUPT(grp))
if (!grp || EXT4_MB_GRP_IBITMAP_CORRUPT(grp))
goto next_group;
}
@ -1183,6 +1183,10 @@ got:
if (!(sbi->s_mount_state & EXT4_FC_REPLAY)) {
grp = ext4_get_group_info(sb, group);
if (!grp) {
err = -EFSCORRUPTED;
goto out;
}
down_read(&grp->alloc_sem); /*
* protect vs itable
* lazyinit
@ -1526,7 +1530,7 @@ int ext4_init_inode_table(struct super_block *sb, ext4_group_t group,
}
gdp = ext4_get_group_desc(sb, group, &group_desc_bh);
if (!gdp)
if (!gdp || !grp)
goto out;
/*

64
fs/ext4/mballoc.c
View File

@ -745,6 +745,8 @@ static int __mb_check_buddy(struct ext4_buddy *e4b, char *file,
MB_CHECK_ASSERT(e4b->bd_info->bb_fragments == fragments);
grp = ext4_get_group_info(sb, e4b->bd_group);
if (!grp)
return NULL;
list_for_each(cur, &grp->bb_prealloc_list) {
ext4_group_t groupnr;
struct ext4_prealloc_space *pa;
@ -1060,9 +1062,9 @@ mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
static noinline_for_stack
void ext4_mb_generate_buddy(struct super_block *sb,
void *buddy, void *bitmap, ext4_group_t group)
void *buddy, void *bitmap, ext4_group_t group,
struct ext4_group_info *grp)
{
struct ext4_group_info *grp = ext4_get_group_info(sb, group);
struct ext4_sb_info *sbi = EXT4_SB(sb);
ext4_grpblk_t max = EXT4_CLUSTERS_PER_GROUP(sb);
ext4_grpblk_t i = 0;
@ -1181,6 +1183,8 @@ static int ext4_mb_init_cache(struct page *page, char *incore, gfp_t gfp)
break;
grinfo = ext4_get_group_info(sb, group);
if (!grinfo)
continue;
/*
* If page is uptodate then we came here after online resize
* which added some new uninitialized group info structs, so
@ -1246,6 +1250,10 @@ static int ext4_mb_init_cache(struct page *page, char *incore, gfp_t gfp)
group, page->index, i * blocksize);
trace_ext4_mb_buddy_bitmap_load(sb, group);
grinfo = ext4_get_group_info(sb, group);
if (!grinfo) {
err = -EFSCORRUPTED;
goto out;
}
grinfo->bb_fragments = 0;
memset(grinfo->bb_counters, 0,
sizeof(*grinfo->bb_counters) *
@ -1256,7 +1264,7 @@ static int ext4_mb_init_cache(struct page *page, char *incore, gfp_t gfp)
ext4_lock_group(sb, group);
/* init the buddy */
memset(data, 0xff, blocksize);
ext4_mb_generate_buddy(sb, data, incore, group);
ext4_mb_generate_buddy(sb, data, incore, group, grinfo);
ext4_unlock_group(sb, group);
incore = NULL;
} else {
@ -1370,6 +1378,9 @@ int ext4_mb_init_group(struct super_block *sb, ext4_group_t group, gfp_t gfp)
might_sleep();
mb_debug(sb, "init group %u\n", group);
this_grp = ext4_get_group_info(sb, group);
if (!this_grp)
return -EFSCORRUPTED;
/*
* This ensures that we don't reinit the buddy cache
* page which map to the group from which we are already
@ -1444,6 +1455,8 @@ ext4_mb_load_buddy_gfp(struct super_block *sb, ext4_group_t group,
blocks_per_page = PAGE_SIZE / sb->s_blocksize;
grp = ext4_get_group_info(sb, group);
if (!grp)
return -EFSCORRUPTED;
e4b->bd_blkbits = sb->s_blocksize_bits;
e4b->bd_info = grp;
@ -2159,6 +2172,8 @@ int ext4_mb_find_by_goal(struct ext4_allocation_context *ac,
struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);
struct ext4_free_extent ex;
if (!grp)
return -EFSCORRUPTED;
if (!(ac->ac_flags & (EXT4_MB_HINT_TRY_GOAL | EXT4_MB_HINT_GOAL_ONLY)))
return 0;
if (grp->bb_free == 0)
@ -2385,7 +2400,7 @@ static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
BUG_ON(cr < 0 || cr >= 4);
if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp) || !grp))
return false;
free = grp->bb_free;
@ -2454,6 +2469,8 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
ext4_grpblk_t free;
int ret = 0;
if (!grp)
return -EFSCORRUPTED;
if (sbi->s_mb_stats)
atomic64_inc(&sbi->s_bal_cX_groups_considered[ac->ac_criteria]);
if (should_lock) {
@ -2534,7 +2551,7 @@ ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group,
* prefetch once, so we avoid getblk() call, which can
* be expensive.
*/
if (!EXT4_MB_GRP_TEST_AND_SET_READ(grp) &&
if (gdp && grp && !EXT4_MB_GRP_TEST_AND_SET_READ(grp) &&
EXT4_MB_GRP_NEED_INIT(grp) &&
ext4_free_group_clusters(sb, gdp) > 0 &&
!(ext4_has_group_desc_csum(sb) &&
@ -2578,7 +2595,7 @@ void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group,
gdp = ext4_get_group_desc(sb, group, NULL);
grp = ext4_get_group_info(sb, group);
if (EXT4_MB_GRP_NEED_INIT(grp) &&
if (grp && gdp && EXT4_MB_GRP_NEED_INIT(grp) &&
ext4_free_group_clusters(sb, gdp) > 0 &&
!(ext4_has_group_desc_csum(sb) &&
(gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))) {
@ -2837,6 +2854,8 @@ static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
sizeof(struct ext4_group_info);
grinfo = ext4_get_group_info(sb, group);
if (!grinfo)
return 0;
/* Load the group info in memory only if not already loaded. */
if (unlikely(EXT4_MB_GRP_NEED_INIT(grinfo))) {
err = ext4_mb_load_buddy(sb, group, &e4b);
@ -2847,7 +2866,7 @@ static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
buddy_loaded = 1;
}
memcpy(&sg, ext4_get_group_info(sb, group), i);
memcpy(&sg, grinfo, i);
if (buddy_loaded)
ext4_mb_unload_buddy(&e4b);
@ -3208,8 +3227,12 @@ static int ext4_mb_init_backend(struct super_block *sb)
err_freebuddy:
cachep = get_groupinfo_cache(sb->s_blocksize_bits);
while (i-- > 0)
kmem_cache_free(cachep, ext4_get_group_info(sb, i));
while (i-- > 0) {
struct ext4_group_info *grp = ext4_get_group_info(sb, i);
if (grp)
kmem_cache_free(cachep, grp);
}
i = sbi->s_group_info_size;
rcu_read_lock();
group_info = rcu_dereference(sbi->s_group_info);
@ -3522,6 +3545,8 @@ int ext4_mb_release(struct super_block *sb)
for (i = 0; i < ngroups; i++) {
cond_resched();
grinfo = ext4_get_group_info(sb, i);
if (!grinfo)
continue;
mb_group_bb_bitmap_free(grinfo);
ext4_lock_group(sb, i);
count = ext4_mb_cleanup_pa(grinfo);
@ -4606,6 +4631,8 @@ static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
struct ext4_free_data *entry;
grp = ext4_get_group_info(sb, group);
if (!grp)
return;
n = rb_first(&(grp->bb_free_root));
while (n) {
@ -4633,6 +4660,9 @@ void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
int preallocated = 0;
int len;
if (!grp)
return;
/* all form of preallocation discards first load group,
* so the only competing code is preallocation use.
* we don't need any locking here
@ -4869,6 +4899,8 @@ adjust_bex:
ei = EXT4_I(ac->ac_inode);
grp = ext4_get_group_info(sb, ac->ac_b_ex.fe_group);
if (!grp)
return;
pa->pa_node_lock.inode_lock = &ei->i_prealloc_lock;
pa->pa_inode = ac->ac_inode;
@ -4918,6 +4950,8 @@ ext4_mb_new_group_pa(struct ext4_allocation_context *ac)
atomic_add(pa->pa_free, &EXT4_SB(sb)->s_mb_preallocated);
grp = ext4_get_group_info(sb, ac->ac_b_ex.fe_group);
if (!grp)
return;
lg = ac->ac_lg;
BUG_ON(lg == NULL);
@ -5043,6 +5077,8 @@ ext4_mb_discard_group_preallocations(struct super_block *sb,
int err;
int free = 0;
if (!grp)
return 0;
mb_debug(sb, "discard preallocation for group %u\n", group);
if (list_empty(&grp->bb_prealloc_list))
goto out_dbg;
@ -5297,6 +5333,9 @@ static inline void ext4_mb_show_pa(struct super_block *sb)
struct ext4_prealloc_space *pa;
ext4_grpblk_t start;
struct list_head *cur;
if (!grp)
continue;
ext4_lock_group(sb, i);
list_for_each(cur, &grp->bb_prealloc_list) {
pa = list_entry(cur, struct ext4_prealloc_space,
@ -6064,6 +6103,7 @@ static void ext4_mb_clear_bb(handle_t *handle, struct inode *inode,
struct buffer_head *bitmap_bh = NULL;
struct super_block *sb = inode->i_sb;
struct ext4_group_desc *gdp;
struct ext4_group_info *grp;
unsigned int overflow;
ext4_grpblk_t bit;
struct buffer_head *gd_bh;
@ -6089,8 +6129,8 @@ do_more:
overflow = 0;
ext4_get_group_no_and_offset(sb, block, &block_group, &bit);
if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(
ext4_get_group_info(sb, block_group))))
grp = ext4_get_group_info(sb, block_group);
if (unlikely(!grp || EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
return;
/*
@ -6692,6 +6732,8 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
for (group = first_group; group <= last_group; group++) {
grp = ext4_get_group_info(sb, group);
if (!grp)
continue;
/* We only do this if the grp has never been initialized */
if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
ret = ext4_mb_init_group(sb, group, GFP_NOFS);

2
fs/ext4/super.c
View File

@ -1048,6 +1048,8 @@ void ext4_mark_group_bitmap_corrupted(struct super_block *sb,
struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, NULL);
int ret;
if (!grp || !gdp)
return;
if (flags & EXT4_GROUP_INFO_BBITMAP_CORRUPT) {
ret = ext4_test_and_set_bit(EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT,
&grp->bb_state);