From: Viacheslav Dubeyko slava@dubeyko.com
[ Upstream commit 736a0516a16268995f4898eded49bfef077af709 ]
The hfs_find_init() method can trigger the crash if tree pointer is NULL:
[ 45.746290][ T9787] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000008: 0000 [#1] SMP KAI [ 45.747287][ T9787] KASAN: null-ptr-deref in range [0x0000000000000040-0x0000000000000047] [ 45.748716][ T9787] CPU: 2 UID: 0 PID: 9787 Comm: repro Not tainted 6.16.0-rc3 #10 PREEMPT(full) [ 45.750250][ T9787] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 45.751983][ T9787] RIP: 0010:hfs_find_init+0x86/0x230 [ 45.752834][ T9787] Code: c1 ea 03 80 3c 02 00 0f 85 9a 01 00 00 4c 8d 6b 40 48 c7 45 18 00 00 00 00 48 b8 00 00 00 00 00 fc [ 45.755574][ T9787] RSP: 0018:ffffc90015157668 EFLAGS: 00010202 [ 45.756432][ T9787] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff819a4d09 [ 45.757457][ T9787] RDX: 0000000000000008 RSI: ffffffff819acd3a RDI: ffffc900151576e8 [ 45.758282][ T9787] RBP: ffffc900151576d0 R08: 0000000000000005 R09: 0000000000000000 [ 45.758943][ T9787] R10: 0000000080000000 R11: 0000000000000001 R12: 0000000000000004 [ 45.759619][ T9787] R13: 0000000000000040 R14: ffff88802c50814a R15: 0000000000000000 [ 45.760293][ T9787] FS: 00007ffb72734540(0000) GS:ffff8880cec64000(0000) knlGS:0000000000000000 [ 45.761050][ T9787] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 45.761606][ T9787] CR2: 00007f9bd8225000 CR3: 000000010979a000 CR4: 00000000000006f0 [ 45.762286][ T9787] Call Trace: [ 45.762570][ T9787] <TASK> [ 45.762824][ T9787] hfs_ext_read_extent+0x190/0x9d0 [ 45.763269][ T9787] ? submit_bio_noacct_nocheck+0x2dd/0xce0 [ 45.763766][ T9787] ? __pfx_hfs_ext_read_extent+0x10/0x10 [ 45.764250][ T9787] hfs_get_block+0x55f/0x830 [ 45.764646][ T9787] block_read_full_folio+0x36d/0x850 [ 45.765105][ T9787] ? __pfx_hfs_get_block+0x10/0x10 [ 45.765541][ T9787] ? const_folio_flags+0x5b/0x100 [ 45.765972][ T9787] ? __pfx_hfs_read_folio+0x10/0x10 [ 45.766415][ T9787] filemap_read_folio+0xbe/0x290 [ 45.766840][ T9787] ? __pfx_filemap_read_folio+0x10/0x10 [ 45.767325][ T9787] ? __filemap_get_folio+0x32b/0xbf0 [ 45.767780][ T9787] do_read_cache_folio+0x263/0x5c0 [ 45.768223][ T9787] ? __pfx_hfs_read_folio+0x10/0x10 [ 45.768666][ T9787] read_cache_page+0x5b/0x160 [ 45.769070][ T9787] hfs_btree_open+0x491/0x1740 [ 45.769481][ T9787] hfs_mdb_get+0x15e2/0x1fb0 [ 45.769877][ T9787] ? __pfx_hfs_mdb_get+0x10/0x10 [ 45.770316][ T9787] ? find_held_lock+0x2b/0x80 [ 45.770731][ T9787] ? lockdep_init_map_type+0x5c/0x280 [ 45.771200][ T9787] ? lockdep_init_map_type+0x5c/0x280 [ 45.771674][ T9787] hfs_fill_super+0x38e/0x720 [ 45.772092][ T9787] ? __pfx_hfs_fill_super+0x10/0x10 [ 45.772549][ T9787] ? snprintf+0xbe/0x100 [ 45.772931][ T9787] ? __pfx_snprintf+0x10/0x10 [ 45.773350][ T9787] ? do_raw_spin_lock+0x129/0x2b0 [ 45.773796][ T9787] ? find_held_lock+0x2b/0x80 [ 45.774215][ T9787] ? set_blocksize+0x40a/0x510 [ 45.774636][ T9787] ? sb_set_blocksize+0x176/0x1d0 [ 45.775087][ T9787] ? setup_bdev_super+0x369/0x730 [ 45.775533][ T9787] get_tree_bdev_flags+0x384/0x620 [ 45.775985][ T9787] ? __pfx_hfs_fill_super+0x10/0x10 [ 45.776453][ T9787] ? __pfx_get_tree_bdev_flags+0x10/0x10 [ 45.776950][ T9787] ? bpf_lsm_capable+0x9/0x10 [ 45.777365][ T9787] ? security_capable+0x80/0x260 [ 45.777803][ T9787] vfs_get_tree+0x8e/0x340 [ 45.778203][ T9787] path_mount+0x13de/0x2010 [ 45.778604][ T9787] ? kmem_cache_free+0x2b0/0x4c0 [ 45.779052][ T9787] ? __pfx_path_mount+0x10/0x10 [ 45.779480][ T9787] ? getname_flags.part.0+0x1c5/0x550 [ 45.779954][ T9787] ? putname+0x154/0x1a0 [ 45.780335][ T9787] __x64_sys_mount+0x27b/0x300 [ 45.780758][ T9787] ? __pfx___x64_sys_mount+0x10/0x10 [ 45.781232][ T9787] do_syscall_64+0xc9/0x480 [ 45.781631][ T9787] entry_SYSCALL_64_after_hwframe+0x77/0x7f [ 45.782149][ T9787] RIP: 0033:0x7ffb7265b6ca [ 45.782539][ T9787] Code: 48 8b 0d c9 17 0d 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 [ 45.784212][ T9787] RSP: 002b:00007ffc0c10cfb8 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5 [ 45.784935][ T9787] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ffb7265b6ca [ 45.785626][ T9787] RDX: 0000200000000240 RSI: 0000200000000280 RDI: 00007ffc0c10d100 [ 45.786316][ T9787] RBP: 00007ffc0c10d190 R08: 00007ffc0c10d000 R09: 0000000000000000 [ 45.787011][ T9787] R10: 0000000000000048 R11: 0000000000000206 R12: 0000560246733250 [ 45.787697][ T9787] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 [ 45.788393][ T9787] </TASK> [ 45.788665][ T9787] Modules linked in: [ 45.789058][ T9787] ---[ end trace 0000000000000000 ]--- [ 45.789554][ T9787] RIP: 0010:hfs_find_init+0x86/0x230 [ 45.790028][ T9787] Code: c1 ea 03 80 3c 02 00 0f 85 9a 01 00 00 4c 8d 6b 40 48 c7 45 18 00 00 00 00 48 b8 00 00 00 00 00 fc [ 45.792364][ T9787] RSP: 0018:ffffc90015157668 EFLAGS: 00010202 [ 45.793155][ T9787] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff819a4d09 [ 45.794123][ T9787] RDX: 0000000000000008 RSI: ffffffff819acd3a RDI: ffffc900151576e8 [ 45.795105][ T9787] RBP: ffffc900151576d0 R08: 0000000000000005 R09: 0000000000000000 [ 45.796135][ T9787] R10: 0000000080000000 R11: 0000000000000001 R12: 0000000000000004 [ 45.797114][ T9787] R13: 0000000000000040 R14: ffff88802c50814a R15: 0000000000000000 [ 45.798024][ T9787] FS: 00007ffb72734540(0000) GS:ffff8880cec64000(0000) knlGS:0000000000000000 [ 45.799019][ T9787] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 45.799822][ T9787] CR2: 00007f9bd8225000 CR3: 000000010979a000 CR4: 00000000000006f0 [ 45.800747][ T9787] Kernel panic - not syncing: Fatal exception
The hfs_fill_super() calls hfs_mdb_get() method that tries to construct Extents Tree and Catalog Tree:
HFS_SB(sb)->ext_tree = hfs_btree_open(sb, HFS_EXT_CNID, hfs_ext_keycmp); if (!HFS_SB(sb)->ext_tree) { pr_err("unable to open extent tree\n"); goto out; } HFS_SB(sb)->cat_tree = hfs_btree_open(sb, HFS_CAT_CNID, hfs_cat_keycmp); if (!HFS_SB(sb)->cat_tree) { pr_err("unable to open catalog tree\n"); goto out; }
However, hfs_btree_open() calls read_mapping_page() that calls hfs_get_block(). And this method calls hfs_ext_read_extent():
static int hfs_ext_read_extent(struct inode *inode, u16 block) { struct hfs_find_data fd; int res;
if (block >= HFS_I(inode)->cached_start && block < HFS_I(inode)->cached_start + HFS_I(inode)->cached_blocks) return 0;
res = hfs_find_init(HFS_SB(inode->i_sb)->ext_tree, &fd); if (!res) { res = __hfs_ext_cache_extent(&fd, inode, block); hfs_find_exit(&fd); } return res; }
The problem here that hfs_find_init() is trying to use HFS_SB(inode->i_sb)->ext_tree that is not initialized yet. It will be initailized when hfs_btree_open() finishes the execution.
The patch adds checking of tree pointer in hfs_find_init() and it reworks the logic of hfs_btree_open() by reading the b-tree's header directly from the volume. The read_mapping_page() is exchanged on filemap_grab_folio() that grab the folio from mapping. Then, sb_bread() extracts the b-tree's header content and copy it into the folio.
Reported-by: Wenzhi Wang wenzhi.wang@uwaterloo.ca Signed-off-by: Viacheslav Dubeyko slava@dubeyko.com cc: John Paul Adrian Glaubitz glaubitz@physik.fu-berlin.de cc: Yangtao Li frank.li@vivo.com cc: linux-fsdevel@vger.kernel.org Link: https://lore.kernel.org/r/20250710213657.108285-1-slava@dubeyko.com Signed-off-by: Viacheslav Dubeyko slava@dubeyko.com Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
**YES**
This commit should be backported to stable kernel trees. Here's my extensive analysis:
## Critical Bug Fix Analysis
This commit fixes a **critical kernel panic** (general protection fault) that can be triggered during normal HFS filesystem operations. The bug represents a serious stability issue that meets stable kernel criteria.
## Root Cause Analysis
The crash occurs due to a **use-before-initialization bug** in the HFS filesystem code:
1. **Initialization Order Issue**: When `hfs_fill_super()` is called, it tries to construct the Extents Tree via: ```c HFS_SB(sb)->ext_tree = hfs_btree_open(sb, HFS_EXT_CNID, hfs_ext_keycmp); ```
2. **Circular Dependency**: During `hfs_btree_open()` execution: - It calls `read_mapping_page()` to read the btree header - This triggers `hfs_get_block()` - Which calls `hfs_ext_read_extent()` - Which tries to use `HFS_SB(inode->i_sb)->ext_tree` via `hfs_find_init()` - But `ext_tree` is NULL because we're still in the process of initializing it!
3. **NULL Pointer Dereference**: The crash stack trace shows: ``` KASAN: null-ptr-deref in range [0x0000000000000040-0x0000000000000047] ``` This occurs when trying to access `tree->max_key_len` at offset 0x40 from a NULL tree pointer.
## Fix Implementation
The patch implements two key fixes:
1. **Defensive Programming**: Adds NULL checks in `hfs_find_init()`: ```c + if (!tree || !fd) + return -EINVAL; ```
2. **Breaking the Circular Dependency**: Reworks `hfs_btree_open()` to avoid the problematic code path: - Replaces `read_mapping_page()` with `filemap_grab_folio()` - Uses `sb_bread()` to read the btree header directly from disk - Avoids going through the extent management code during initialization
## Backport Justification
This commit meets all stable kernel criteria:
1. **Fixes a Real Bug**: Prevents a kernel panic that can be triggered during normal filesystem operations 2. **Small and Contained**: The changes are limited to HFS filesystem code with no impact on other subsystems 3. **Clear Fix**: The solution directly addresses the root cause without architectural changes 4. **No New Features**: Only fixes the existing bug without adding functionality 5. **High Impact**: Kernel panics are critical issues that affect system stability 6. **Minimal Risk**: Changes are confined to HFS subsystem with clear boundaries
## Additional Context
- The commit includes a detailed crash trace showing this is a real- world issue - Recent commit history shows HFS has had multiple similar stability fixes (slab-out-of-bounds, OOB reads/writes) - The fix follows established patterns for handling initialization order issues - The reporter is credited (Wenzhi Wang from University of Waterloo), indicating this was found through testing/research
This is exactly the type of bug fix that stable kernels exist to incorporate - preventing kernel crashes without introducing new risks.
fs/hfs/bfind.c | 3 +++ fs/hfs/btree.c | 57 +++++++++++++++++++++++++++++++++++++++---------- fs/hfs/extent.c | 2 +- fs/hfs/hfs_fs.h | 1 + 4 files changed, 51 insertions(+), 12 deletions(-)
diff --git a/fs/hfs/bfind.c b/fs/hfs/bfind.c index ef9498a6e88a..34e9804e0f36 100644 --- a/fs/hfs/bfind.c +++ b/fs/hfs/bfind.c @@ -16,6 +16,9 @@ int hfs_find_init(struct hfs_btree *tree, struct hfs_find_data *fd) { void *ptr;
+ if (!tree || !fd) + return -EINVAL; + fd->tree = tree; fd->bnode = NULL; ptr = kmalloc(tree->max_key_len * 2 + 4, GFP_KERNEL); diff --git a/fs/hfs/btree.c b/fs/hfs/btree.c index 2fa4b1f8cc7f..e86e1e235658 100644 --- a/fs/hfs/btree.c +++ b/fs/hfs/btree.c @@ -21,8 +21,12 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id, btree_keycmp ke struct hfs_btree *tree; struct hfs_btree_header_rec *head; struct address_space *mapping; - struct page *page; + struct folio *folio; + struct buffer_head *bh; unsigned int size; + u16 dblock; + sector_t start_block; + loff_t offset;
tree = kzalloc(sizeof(*tree), GFP_KERNEL); if (!tree) @@ -75,12 +79,40 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id, btree_keycmp ke unlock_new_inode(tree->inode);
mapping = tree->inode->i_mapping; - page = read_mapping_page(mapping, 0, NULL); - if (IS_ERR(page)) + folio = filemap_grab_folio(mapping, 0); + if (IS_ERR(folio)) goto free_inode;
+ folio_zero_range(folio, 0, folio_size(folio)); + + dblock = hfs_ext_find_block(HFS_I(tree->inode)->first_extents, 0); + start_block = HFS_SB(sb)->fs_start + (dblock * HFS_SB(sb)->fs_div); + + size = folio_size(folio); + offset = 0; + while (size > 0) { + size_t len; + + bh = sb_bread(sb, start_block); + if (!bh) { + pr_err("unable to read tree header\n"); + goto put_folio; + } + + len = min_t(size_t, folio_size(folio), sb->s_blocksize); + memcpy_to_folio(folio, offset, bh->b_data, sb->s_blocksize); + + brelse(bh); + + start_block++; + offset += len; + size -= len; + } + + folio_mark_uptodate(folio); + /* Load the header */ - head = (struct hfs_btree_header_rec *)(kmap_local_page(page) + + head = (struct hfs_btree_header_rec *)(kmap_local_folio(folio, 0) + sizeof(struct hfs_bnode_desc)); tree->root = be32_to_cpu(head->root); tree->leaf_count = be32_to_cpu(head->leaf_count); @@ -95,22 +127,22 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id, btree_keycmp ke
size = tree->node_size; if (!is_power_of_2(size)) - goto fail_page; + goto fail_folio; if (!tree->node_count) - goto fail_page; + goto fail_folio; switch (id) { case HFS_EXT_CNID: if (tree->max_key_len != HFS_MAX_EXT_KEYLEN) { pr_err("invalid extent max_key_len %d\n", tree->max_key_len); - goto fail_page; + goto fail_folio; } break; case HFS_CAT_CNID: if (tree->max_key_len != HFS_MAX_CAT_KEYLEN) { pr_err("invalid catalog max_key_len %d\n", tree->max_key_len); - goto fail_page; + goto fail_folio; } break; default: @@ -121,12 +153,15 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id, btree_keycmp ke tree->pages_per_bnode = (tree->node_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
kunmap_local(head); - put_page(page); + folio_unlock(folio); + folio_put(folio); return tree;
-fail_page: +fail_folio: kunmap_local(head); - put_page(page); +put_folio: + folio_unlock(folio); + folio_put(folio); free_inode: tree->inode->i_mapping->a_ops = &hfs_aops; iput(tree->inode); diff --git a/fs/hfs/extent.c b/fs/hfs/extent.c index 4a0ce131e233..580c62981dbd 100644 --- a/fs/hfs/extent.c +++ b/fs/hfs/extent.c @@ -71,7 +71,7 @@ int hfs_ext_keycmp(const btree_key *key1, const btree_key *key2) * * Find a block within an extent record */ -static u16 hfs_ext_find_block(struct hfs_extent *ext, u16 off) +u16 hfs_ext_find_block(struct hfs_extent *ext, u16 off) { int i; u16 count; diff --git a/fs/hfs/hfs_fs.h b/fs/hfs/hfs_fs.h index a0c7cb0f79fc..732c5c4c7545 100644 --- a/fs/hfs/hfs_fs.h +++ b/fs/hfs/hfs_fs.h @@ -190,6 +190,7 @@ extern const struct inode_operations hfs_dir_inode_operations;
/* extent.c */ extern int hfs_ext_keycmp(const btree_key *, const btree_key *); +extern u16 hfs_ext_find_block(struct hfs_extent *ext, u16 off); extern int hfs_free_fork(struct super_block *, struct hfs_cat_file *, int); extern int hfs_ext_write_extent(struct inode *); extern int hfs_extend_file(struct inode *);