title: fs,hugetlb: fix NULL pointer dereference in hugetlbs_fill_super
description: In the Linux kernel, the following vulnerability has been resolved:
fs,hugetlb: fix NULL pointer dereference in hugetlbs_fill_super
When configuring a hugetlb filesystem via the fsconfig() syscall, there is
a possible NULL dereference in hugetlbfs_fill_super() caused by assigning
NULL to ctx->hstate in hugetlbfs_parse_param() when the requested pagesize
is non valid.
E.g: Taking the following steps:
fd = fsopen("hugetlbfs", FSOPEN_CLOEXEC);
fsconfig(fd, FSCONFIG_SET_STRING, "pagesize", "1024", 0);
fsconfig(fd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
Given that the requested "pagesize" is invalid, ctxt->hstate will be replaced
with NULL, losing its previous value, and we will print an error:
...
...
case Opt_pagesize:
ps = memparse(param->string, &rest);
ctx->hstate = h;
if (!ctx->hstate) {
pr_err("Unsupported page size %lu MB\n", ps / SZ_1M);
return -EINVAL;
}
return 0;
...
...
This is a problem because later on, we will dereference ctxt->hstate in
hugetlbfs_fill_super()
...
...
sb->s_blocksize = huge_page_size(ctx->hstate);
...
...
Causing below Oops.
Fix this by replacing cxt->hstate value only when then pagesize is known
to be valid.
kernel: hugetlbfs: Unsupported page size 0 MB
kernel: BUG: kernel NULL pointer dereference, address: 0000000000000028
kernel: #PF: supervisor read access in kernel mode
kernel: #PF: error_code(0x0000) - not-present page
kernel: PGD 800000010f66c067 P4D 800000010f66c067 PUD 1b22f8067 PMD 0
kernel: Oops: 0000 [#1] PREEMPT SMP PTI
kernel: CPU: 4 PID: 5659 Comm: syscall Tainted: G            E      6.8.0-rc2-default+ #22 5a47c3fef76212addcc6eb71344aabc35190ae8f
kernel: Hardware name: Intel Corp. GROVEPORT/GROVEPORT, BIOS GVPRCRB1.86B.0016.D04.1705030402 05/03/2017
kernel: RIP: 0010:hugetlbfs_fill_super+0xb4/0x1a0
kernel: Code: 48 8b 3b e8 3e c6 ed ff 48 85 c0 48 89 45 20 0f 84 d6 00 00 00 48 b8 ff ff ff ff ff ff ff 7f 4c 89 e7 49 89 44 24 20 48 8b 03 <8b> 48 28 b8 00 10 00 00 48 d3 e0 49 89 44 24 18 48 8b 03 8b 40 28
kernel: RSP: 0018:ffffbe9960fcbd48 EFLAGS: 00010246
kernel: RAX: 0000000000000000 RBX: ffff9af5272ae780 RCX: 0000000000372004
kernel: RDX: ffffffffffffffff RSI: ffffffffffffffff RDI: ffff9af555e9b000
kernel: RBP: ffff9af52ee66b00 R08: 0000000000000040 R09: 0000000000370004
kernel: R10: ffffbe9960fcbd48 R11: 0000000000000040 R12: ffff9af555e9b000
kernel: R13: ffffffffa66b86c0 R14: ffff9af507d2f400 R15: ffff9af507d2f400
kernel: FS:  00007ffbc0ba4740(0000) GS:ffff9b0bd7000000(0000) knlGS:0000000000000000
kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
kernel: CR2: 0000000000000028 CR3: 00000001b1ee0000 CR4: 00000000001506f0
kernel: Call Trace:
kernel:  <TASK>
kernel:  ? __die_body+0x1a/0x60
kernel:  ? page_fault_oops+0x16f/0x4a0
kernel:  ? search_bpf_extables+0x65/0x70
kernel:  ? fixup_exception+0x22/0x310
kernel:  ? exc_page_fault+0x69/0x150
kernel:  ? asm_exc_page_fault+0x22/0x30
kernel:  ? __pfx_hugetlbfs_fill_super+0x10/0x10
kernel:  ? hugetlbfs_fill_super+0xb4/0x1a0
kernel:  ? hugetlbfs_fill_super+0x28/0x1a0
kernel:  ? __pfx_hugetlbfs_fill_super+0x10/0x10
kernel:  vfs_get_super+0x40/0xa0
kernel:  ? __pfx_bpf_lsm_capable+0x10/0x10
kernel:  vfs_get_tree+0x25/0xd0
kernel:  vfs_cmd_create+0x64/0xe0
kernel:  __x64_sys_fsconfig+0x395/0x410
kernel:  do_syscall_64+0x80/0x160
kernel:  ? syscall_exit_to_user_mode+0x82/0x240
kernel:  ? do_syscall_64+0x8d/0x160
kernel:  ? syscall_exit_to_user_mode+0x82/0x240
kernel:  ? do_syscall_64+0x8d/0x160
kernel:  ? exc_page_fault+0x69/0x150
kernel:  entry_SYSCALL_64_after_hwframe+0x6e/0x76
kernel: RIP: 0033:0x7ffbc0cb87c9
kernel: Code: 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 66 90 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 8b 0d 97 96 0d 00 f7 d8 64 89 01 48
kernel: RSP: 002b:00007ffc29d2f388 EFLAGS: 00000206 ORIG_RAX: 00000000000001af
kernel: RAX: fffffffffff
---truncated---
affected:
{
product: Linux
vendor: Linux
defaultStatus: unaffected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 32021982a324, lessThan: 1dde8ef4b7a7, status: affected, versionType: git
version: 32021982a324, lessThan: 80d852299987, status: affected, versionType: git
version: 32021982a324, lessThan: 22850c9950a4, status: affected, versionType: git
version: 32021982a324, lessThan: 2e2c07104b49, status: affected, versionType: git
version: 32021982a324, lessThan: 13c5a9fb0710, status: affected, versionType: git
version: 32021982a324, lessThan: ec78418801ef, status: affected, versionType: git
version: 32021982a324, lessThan: 79d72c68c587, status: affected, versionType: git
}
{
product: Linux
vendor: Linux
defaultStatus: affected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 5.1, status: affected
version: 0, lessThan: 5.1, status: unaffected, versionType: custom
version: 5.4.271, lessThanOrEqual: 5.4.*, status: unaffected, versionType: custom
version: 5.10.212, lessThanOrEqual: 5.10.*, status: unaffected, versionType: custom
version: 5.15.151, lessThanOrEqual: 5.15.*, status: unaffected, versionType: custom
version: 6.1.79, lessThanOrEqual: 6.1.*, status: unaffected, versionType: custom
version: 6.6.18, lessThanOrEqual: 6.6.*, status: unaffected, versionType: custom
version: 6.7.6, lessThanOrEqual: 6.7.*, status: unaffected, versionType: custom
version: 6.8, lessThanOrEqual: *, status: unaffected, versionType: original_commit_for_fix
}
