[PATCH v3] fs/ceph/file: fix buffer overflow in __ceph_sync_read()

From: Max Kellermann
Date: Wed Nov 27 2024 - 16:21:45 EST

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If the inode size gets truncated by another task, __ceph_sync_read()
may crash with a buffer overflow because it sets `left` to a huge
value:

else if (off + ret > i_size)
left = i_size - off;

Imagine `i_size` was truncated to zero; `off + ret > i_size` is always
true, but `i_size - off` can be negative; since `left` is unsigned, it
turns into a rather huge number, and thus the `while (left > 0)` loop
never stops until it eventually crashes because `pages[idx]` overflows
the `pages` allocation.

We need to ensure that `i_size` never becomes smaller than `off`. I
suggest breaking from the loop as soon as this happens, right after
the `i_size = i_size_read(inode)` update.

This can be reproduced easily by running a program like this on one
Ceph client:

ioctl(fd, CEPH_IOC_SYNCIO);
char buffer[16384];
while (1) pread(fd, buffer, sizeof(buffer), 8192);

Then, on another server, truncate and rewrite the file until the first
server's kernel crashes (I never needed more than two attempts to
trigger the kernel crash):

dd if=/dev/urandom of=foo bs=1k count=64

This is how the crash looks like (with KASAN and some debug logs from
`__ceph_sync_read` and `ceph_fill_file_size`):

ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] ceph_fill_file_size: truncate_size 0 -> 0, encrypted 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: 8192~16384 got 16384 i_size 65536
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: result 16384 retry_op 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] ceph_fill_file_size: truncate_size 0 -> 0, encrypted 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] ceph_fill_file_size: truncate_size 0 -> 0, encrypted 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] ceph_fill_file_size: size 65536 -> 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] ceph_fill_file_size: truncate_seq 36656 -> 36657
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] ceph_fill_file_size: truncate_size 0 -> 0, encrypted 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] ceph_fill_file_size: truncate_size 0 -> 0, encrypted 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: on inode 0000000035059a6f 1000235edb7.fffffffffffffffe 2000~4000
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: orig 8192~16384 reading 8192~16384
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] ceph_fill_file_size: truncate_size 0 -> 0, encrypted 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: 8192~16384 got 0 i_size 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: result 0 retry_op 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: on inode 0000000035059a6f 1000235edb7.fffffffffffffffe 2000~4000
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: orig 8192~16384 reading 8192~16384
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: 8192~16384 got 0 i_size 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: result 0 retry_op 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: on inode 0000000035059a6f 1000235edb7.fffffffffffffffe 2000~4000
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: orig 8192~16384 reading 8192~16384
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] ceph_fill_file_size: truncate_size 0 -> 0, encrypted 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: 8192~16384 got 0 i_size 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: result 0 retry_op 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: on inode 0000000035059a6f 1000235edb7.fffffffffffffffe 2000~4000
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: orig 8192~16384 reading 8192~16384
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: 8192~16384 got 0 i_size 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: result 0 retry_op 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: on inode 0000000035059a6f 1000235edb7.fffffffffffffffe 2000~4000
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: orig 8192~16384 reading 8192~16384
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: 8192~16384 got 0 i_size 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: result 0 retry_op 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: on inode 0000000035059a6f 1000235edb7.fffffffffffffffe 2000~4000
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: orig 8192~16384 reading 8192~16384
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: 8192~16384 got 0 i_size 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: result 0 retry_op 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: on inode 0000000035059a6f 1000235edb7.fffffffffffffffe 2000~4000
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: orig 8192~16384 reading 8192~16384
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: 8192~16384 got 0 i_size 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: result 0 retry_op 0
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: on inode 0000000035059a6f 1000235edb7.fffffffffffffffe 2000~4000
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: orig 8192~16384 reading 8192~16384
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] __ceph_sync_read: 8192~16384 got 1024 i_size 0
==================================================================
BUG: KASAN: slab-out-of-bounds in __ceph_sync_read+0x173f/0x1b10
Read of size 8 at addr ffff8881d5dfbea0 by task pread/3276

CPU: 3 UID: 2147488069 PID: 3276 Comm: pread Not tainted 6.11.10-cm4all1-hp+ #254
Hardware name: HPE ProLiant DL380 Gen10/ProLiant DL380 Gen10, BIOS U30 09/05/2019
Call Trace:
<TASK>
dump_stack_lvl+0x62/0x90
print_report+0xc4/0x5e0
? __virt_addr_valid+0x1e9/0x3a0
? __ceph_sync_read+0x173f/0x1b10
kasan_report+0xb9/0xf0
? __ceph_sync_read+0x173f/0x1b10
__ceph_sync_read+0x173f/0x1b10
? __pfx___ceph_sync_read+0x10/0x10
? lock_acquire+0x186/0x4d0
? ceph_read_iter+0xace/0x19f0
ceph_read_iter+0xace/0x19f0
? lock_release+0x648/0xb50
? __pfx_ceph_read_iter+0x10/0x10
? __rseq_handle_notify_resume+0x8ed/0xd40
? __pfx___rseq_handle_notify_resume+0x10/0x10
? vfs_read+0x6e0/0xba0
vfs_read+0x6e0/0xba0
? __pfx_vfs_read+0x10/0x10
? syscall_exit_to_user_mode+0x9a/0x190
? syscall_exit_to_user_mode+0x9a/0x190
__x64_sys_pread64+0x19b/0x1f0
? __pfx___x64_sys_pread64+0x10/0x10
? __pfx___rseq_handle_notify_resume+0x10/0x10
do_syscall_64+0x82/0x130
? lockdep_hardirqs_on_prepare+0x275/0x3e0
? syscall_exit_to_user_mode+0x9a/0x190
? do_syscall_64+0x8e/0x130
? do_syscall_64+0x8e/0x130
? lockdep_hardirqs_on_prepare+0x275/0x3e0
? syscall_exit_to_user_mode+0x9a/0x190
? do_syscall_64+0x8e/0x130
? do_syscall_64+0x8e/0x130
? syscall_exit_to_user_mode+0x9a/0x190
? do_syscall_64+0x8e/0x130
entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7f8449d18343
Code: 48 8b 6c 24 48 e8 3d 00 f3 ff 41 b8 02 00 00 00 e9 38 f6 ff ff 66 90 80 3d a1 42 0e 00 00 49 89 ca 74 14 b8 11 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 5d c3 0f 1f 40 00 48 83 ec 28 48 89 54 24 10
RSP: 002b:00007ffd7a2e8b78 EFLAGS: 00000202 ORIG_RAX: 0000000000000011
RAX: ffffffffffffffda RBX: 00007ffd7a2e8cc8 RCX: 00007f8449d18343
RDX: 0000000000004000 RSI: 0000557f7917c2a0 RDI: 0000000000000003
RBP: 00007ffd7a2e8bb0 R08: 0000557f7919d000 R09: 0000000000021001
R10: 0000000000002000 R11: 0000000000000202 R12: 0000000000000000
R13: 00007ffd7a2e8cf0 R14: 0000557f436c2dd8 R15: 00007f8449e43020
</TASK>

Allocated by task 3276:
kasan_save_stack+0x1c/0x40
kasan_save_track+0x10/0x30
__kasan_kmalloc+0x8b/0x90
__kmalloc_noprof+0x1bf/0x490
ceph_alloc_page_vector+0x36/0x110
__ceph_sync_read+0x769/0x1b10
ceph_read_iter+0xace/0x19f0
vfs_read+0x6e0/0xba0
__x64_sys_pread64+0x19b/0x1f0
do_syscall_64+0x82/0x130
entry_SYSCALL_64_after_hwframe+0x76/0x7e

The buggy address belongs to the object at ffff8881d5dfbe80
which belongs to the cache kmalloc-32 of size 32
The buggy address is located 0 bytes to the right of
allocated 32-byte region [ffff8881d5dfbe80, ffff8881d5dfbea0)

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1d5dfb
flags: 0x2fffc0000000000(node=0|zone=2|lastcpupid=0x3fff)
page_type: 0xfdffffff(slab)
raw: 02fffc0000000000 ffff888100042780 dead000000000122 0000000000000000
raw: 0000000000000000 0000000080400040 00000001fdffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8881d5dfbd80: fa fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
ffff8881d5dfbe00: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc
>ffff8881d5dfbe80: 00 00 00 00 fc fc fc fc fa fb fb fb fc fc fc fc
^
ffff8881d5dfbf00: fc fc fc fc fc fc fc fc fa fb fb fb fc fc fc fc
ffff8881d5dfbf80: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc
==================================================================
Disabling lock debugging due to kernel taint
Oops: general protection fault, probably for non-canonical address 0xe021fc6b8000019a: 0000 [#1] SMP KASAN PTI
KASAN: maybe wild-memory-access in range [0x0110035c00000cd0-0x0110035c00000cd7]
CPU: 3 UID: 2147488069 PID: 3276 Comm: pread Tainted: G B 6.11.10-cm4all1-hp+ #254
Tainted: [B]=BAD_PAGE
Hardware name: HPE ProLiant DL380 Gen10/ProLiant DL380 Gen10, BIOS U30 09/05/2019
RIP: 0010:__ceph_sync_read+0xc33/0x1b10
Code: 39 e7 4d 0f 47 fc 48 8d 0c c6 48 89 c8 48 c1 e8 03 42 80 3c 30 00 0f 85 0b 0b 00 00 48 8b 11 48 8d 7a 08 48 89 f8 48 c1 e8 03 <42> 80 3c 30 00 0f 85 0d 0b 00 00 48 8b 42 08 a8 01 0f 84 ee 04 00
RSP: 0018:ffff8881ed6e78e0 EFLAGS: 00010207
RAX: 0022006b8000019a RBX: 0000000000000000 RCX: ffff8881d5dfbea0
RDX: 0110035c00000ccc RSI: 0000000000000008 RDI: 0110035c00000cd4
RBP: ffff8881ed6e7a80 R08: 0000000000000001 R09: fffffbfff28b44ac
R10: ffffffff945a2567 R11: 0000000000000001 R12: ffffffffffffa000
R13: 0000000000000004 R14: dffffc0000000000 R15: 0000000000001000
FS: 00007f8449c1f740(0000) GS:ffff88d2b5a00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb72c6aecf0 CR3: 00000001ed7b6003 CR4: 00000000007706f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
<TASK>
? die_addr+0x3c/0xa0
? exc_general_protection+0x113/0x200
? asm_exc_general_protection+0x22/0x30
? __ceph_sync_read+0xc33/0x1b10
? __pfx___ceph_sync_read+0x10/0x10
? lock_acquire+0x186/0x4d0
? ceph_read_iter+0xace/0x19f0
ceph_read_iter+0xace/0x19f0
? lock_release+0x648/0xb50
? __pfx_ceph_read_iter+0x10/0x10
? __rseq_handle_notify_resume+0x8ed/0xd40
? __pfx___rseq_handle_notify_resume+0x10/0x10
? vfs_read+0x6e0/0xba0
vfs_read+0x6e0/0xba0
? __pfx_vfs_read+0x10/0x10
? syscall_exit_to_user_mode+0x9a/0x190
? syscall_exit_to_user_mode+0x9a/0x190
__x64_sys_pread64+0x19b/0x1f0
? __pfx___x64_sys_pread64+0x10/0x10
? __pfx___rseq_handle_notify_resume+0x10/0x10
do_syscall_64+0x82/0x130
? lockdep_hardirqs_on_prepare+0x275/0x3e0
? syscall_exit_to_user_mode+0x9a/0x190
? do_syscall_64+0x8e/0x130
? do_syscall_64+0x8e/0x130
? lockdep_hardirqs_on_prepare+0x275/0x3e0
? syscall_exit_to_user_mode+0x9a/0x190
? do_syscall_64+0x8e/0x130
? do_syscall_64+0x8e/0x130
? syscall_exit_to_user_mode+0x9a/0x190
? do_syscall_64+0x8e/0x130
entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7f8449d18343
Code: 48 8b 6c 24 48 e8 3d 00 f3 ff 41 b8 02 00 00 00 e9 38 f6 ff ff 66 90 80 3d a1 42 0e 00 00 49 89 ca 74 14 b8 11 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 5d c3 0f 1f 40 00 48 83 ec 28 48 89 54 24 10
RSP: 002b:00007ffd7a2e8b78 EFLAGS: 00000202 ORIG_RAX: 0000000000000011
RAX: ffffffffffffffda RBX: 00007ffd7a2e8cc8 RCX: 00007f8449d18343
RDX: 0000000000004000 RSI: 0000557f7917c2a0 RDI: 0000000000000003
RBP: 00007ffd7a2e8bb0 R08: 0000557f7919d000 R09: 0000000000021001
R10: 0000000000002000 R11: 0000000000000202 R12: 0000000000000000
R13: 00007ffd7a2e8cf0 R14: 0000557f436c2dd8 R15: 00007f8449e43020
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__ceph_sync_read+0xc33/0x1b10
Code: 39 e7 4d 0f 47 fc 48 8d 0c c6 48 89 c8 48 c1 e8 03 42 80 3c 30 00 0f 85 0b 0b 00 00 48 8b 11 48 8d 7a 08 48 89 f8 48 c1 e8 03 <42> 80 3c 30 00 0f 85 0d 0b 00 00 48 8b 42 08 a8 01 0f 84 ee 04 00
RSP: 0018:ffff8881ed6e78e0 EFLAGS: 00010207
RAX: 0022006b8000019a RBX: 0000000000000000 RCX: ffff8881d5dfbea0
RDX: 0110035c00000ccc RSI: 0000000000000008 RDI: 0110035c00000cd4
RBP: ffff8881ed6e7a80 R08: 0000000000000001 R09: fffffbfff28b44ac
R10: ffffffff945a2567 R11: 0000000000000001 R12: ffffffffffffa000
R13: 0000000000000004 R14: dffffc0000000000 R15: 0000000000001000
FS: 00007f8449c1f740(0000) GS:ffff88d2b5a00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb72c6aecf0 CR3: 00000001ed7b6003 CR4: 00000000007706f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
workqueue: ceph_con_workfn hogged CPU for >10000us 35 times, consider switching to WQ_UNBOUND
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] ceph_fill_file_size: size 0 -> 65536
ceph: [8f7ec2f3-0dcb-468f-bd16-37e0a61bf195 4098067] ceph_fill_file_size: truncate_size 0 -> 0, encrypted 0

Fixes: 1065da21e5df ("ceph: stop copying to iter at EOF on sync reads")
Fixes: https://tracker.ceph.com/issues/67524
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Max Kellermann <max.kellermann@xxxxxxxxx>
---
v2: public posting; added link to Ceph bug tracker (vulnerability had
been known already for 3 months)
v3: memory leak fix
---
fs/ceph/file.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 4b8d59ebda00..1f0aed6cd9d5 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -1154,6 +1154,16 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos,
doutc(cl, "%llu~%llu got %zd i_size %llu%s\n", off, len,
ret, i_size, (more ? " MORE" : ""));

+ if (off >= i_size) {
+ /* meanwhile, the file has been truncated by
+ * another task and the offset is no longer
+ * valid; stop here
+ */
+ ceph_release_page_vector(pages, num_pages);
+ ceph_osdc_put_request(req);
+ break;
+ }
+
/* Fix it to go to end of extent map */
if (sparse && ret >= 0)
ret = ceph_sparse_ext_map_end(op);
--
2.45.2

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