Dear developers and maintainers, We encountered a kernel warning in the function disksize_store during testing using our modified syzkaller. It is tested against the latest upstream linux (6.9-rc3). C repro and kernel config are attached to this email. Kernel log is listed below. ``` ------------[ cut here ]------------ WARNING: CPU: 1 PID: 8117 at mm/vmalloc.c:3247 __vmalloc_node_range+0x10a0/0x1490 mm/vmalloc.c:3247 Modules linked in: CPU: 1 PID: 8117 Comm: syz-executor233 Not tainted 6.7.0-rc7 #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:__vmalloc_node_range+0x10a0/0x1490 mm/vmalloc.c:3247 Code: 65 48 2b 04 25 28 00 00 00 0f 85 98 02 00 00 48 81 c4 70 01 00 00 4c 89 e0 5b 5d 41 5c 41 5d 41 5e 41 5f c3 e8 e1 47 b7 ff 90 <0f> 0b 90 45 31 e4 eb a1 e8 d3 47 b7 ff 48 8b 4c 24 40 31 f6 45 31 RSP: 0018:ffffc90002a1fa88 EFLAGS: 00010293 RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffffffff81cdbd54 RDX: ffff88802080a4c0 RSI: ffffffff81cdcd2f RDI: 0000000000000007 RBP: 0000000000000000 R08: 0000000000000007 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000001 R12: ffff8880176b2fe8 R13: 0000000000000000 R14: 0000000000000000 R15: ffff88801a85a918 FS: 00005555559e03c0(0000) GS:ffff888135c00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000020000260 CR3: 000000010c948000 CR4: 0000000000750ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <TASK> __vmalloc_node mm/vmalloc.c:3385 [inline] vzalloc+0x6b/0x80 mm/vmalloc.c:3458 zram_meta_alloc drivers/block/zram/zram_drv.c:1233 [inline] disksize_store+0x10a/0x5b0 drivers/block/zram/zram_drv.c:2031 dev_attr_store+0x54/0x80 drivers/base/core.c:2366 sysfs_kf_write+0x114/0x170 fs/sysfs/file.c:136 kernfs_fop_write_iter+0x337/0x500 fs/kernfs/file.c:334 call_write_iter include/linux/fs.h:2020 [inline] new_sync_write fs/read_write.c:491 [inline] vfs_write+0x96a/0xd80 fs/read_write.c:584 ksys_write+0x122/0x250 fs/read_write.c:637 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x63/0x6b RIP: 0033:0x7f652768bfcd Code: 28 c3 e8 26 1f 00 00 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffed7908618 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007ffed7908818 RCX: 00007f652768bfcd RDX: 0000000000000015 RSI: 0000000020000280 RDI: 0000000000000003 RBP: 0000000000000001 R08: 0000000000000000 R09: 00007ffed7908818 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 R13: 00007ffed7908808 R14: 00007f6527709530 R15: 0000000000000001 </TASK> ``` We analyzed the root cause of this warning. Argument char *buf is a user controlled string, which could be an arbitrary large number (in this case is "18446744073709551615", which is -1 in unsigned long long). Function memparse() in line 2018 calls simple_strtoull() to convert this string into an unsigned long number, so that disksize bypass the check in the next line. After the PAGE_ALIGN, disksize is overflowed and turns to zero. disksize then be passed to zram_meta_alloc(), causing a zero-size vmalloc. One possible fix is to lift PAGE_ALIGN right after memparse(), so that the check would not be bypassed. If you have any questions, please contact us. Reported by: Yue Sun <samsun1006219@xxxxxxxxx> Reported by: xingwei lee <xrivendell7@xxxxxxxxx> Best Regards, Yue
Attachment:
config
Description: Binary data
#define _GNU_SOURCE
#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
uint64_t r[1] = {0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000ul, /*prot=*/0ul,
/*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1,
/*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x20000000ul, /*len=*/0x1000000ul,
/*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/ 7ul,
/*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1,
/*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x21000000ul, /*len=*/0x1000ul, /*prot=*/0ul,
/*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1,
/*offset=*/0ul);
intptr_t res = 0;
memcpy((void*)0x20000240, "/sys/devices/virtual/block/zram0/disksize\000",
42);
res = syscall(__NR_openat, /*fd=*/0xffffffffffffff9cul, /*file=*/0x20000240ul,
/*flags=*/2ul, /*mode=*/0ul);
if (res != -1)
r[0] = res;
sprintf((char*)0x20000280, "%020llu", (long long)-1);
*(uint8_t*)0x20000294 = 0;
syscall(__NR_write, /*fd=*/r[0], /*buf=*/0x20000280ul, /*len=*/0x15ul);
return 0;
}
