[PATCH] secretmem: fix unhandled fault in truncate
From: Mike Rapoport
Date: Thu Jun 30 2022 - 04:26:37 EST
syzkaller reports the following issue:
BUG: unable to handle page fault for address: ffff888021f7e005
PGD 11401067 P4D 11401067 PUD 11402067 PMD 21f7d063 PTE 800fffffde081060
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 3761 Comm: syz-executor281 Not tainted 5.19.0-rc4-syzkaller-00014-g941e3e791269 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:memset_erms+0x9/0x10 arch/x86/lib/memset_64.S:64
Code: c1 e9 03 40 0f b6 f6 48 b8 01 01 01 01 01 01 01 01 48 0f af c6 f3 48 ab 89 d1 f3 aa 4c 89 c8 c3 90 49 89 f9 40 88 f0 48 89 d1 <f3> aa 4c 89 c8 c3 90 49 89 fa 40 0f b6 ce 48 b8 01 01 01 01 01 01
RSP: 0018:ffffc9000329fa90 EFLAGS: 00010202
RAX: 0000000000000000 RBX: 0000000000001000 RCX: 0000000000000ffb
RDX: 0000000000000ffb RSI: 0000000000000000 RDI: ffff888021f7e005
RBP: ffffea000087df80 R08: 0000000000000001 R09: ffff888021f7e005
R10: ffffed10043efdff R11: 0000000000000000 R12: 0000000000000005
R13: 0000000000000000 R14: 0000000000001000 R15: 0000000000000ffb
FS: 00007fb29d8b2700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff888021f7e005 CR3: 0000000026e7b000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
zero_user_segments include/linux/highmem.h:272 [inline]
folio_zero_range include/linux/highmem.h:428 [inline]
truncate_inode_partial_folio+0x76a/0xdf0 mm/truncate.c:237
truncate_inode_pages_range+0x83b/0x1530 mm/truncate.c:381
truncate_inode_pages mm/truncate.c:452 [inline]
truncate_pagecache+0x63/0x90 mm/truncate.c:753
simple_setattr+0xed/0x110 fs/libfs.c:535
secretmem_setattr+0xae/0xf0 mm/secretmem.c:170
notify_change+0xb8c/0x12b0 fs/attr.c:424
do_truncate+0x13c/0x200 fs/open.c:65
do_sys_ftruncate+0x536/0x730 fs/open.c:193
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x46/0xb0
RIP: 0033:0x7fb29d900899
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 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 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fb29d8b2318 EFLAGS: 00000246 ORIG_RAX: 000000000000004d
RAX: ffffffffffffffda RBX: 00007fb29d988408 RCX: 00007fb29d900899
RDX: 00007fb29d900899 RSI: 0000000000000005 RDI: 0000000000000003
RBP: 00007fb29d988400 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb29d98840c
R13: 00007ffca01a23bf R14: 00007fb29d8b2400 R15: 0000000000022000
</TASK>
Modules linked in:
CR2: ffff888021f7e005
---[ end trace 0000000000000000 ]---
Eric Biggers suggested that this happens when
secretmem_setattr()->simple_setattr() races with secretmem_fault() so
that a page that is faulted in by secretmem_fault() (and thus removed
from the direct map) is zeroed by inode truncation right afterwards.
Use an rw_semaphore to make secretmem_fault() and secretmem_setattr()
mutually exclusive.
Reported-by: syzbot+9bd2b7adbd34b30b87e4@xxxxxxxxxxxxxxxxxxxxxxxxx
Suggested-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
---
mm/secretmem.c | 48 ++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 40 insertions(+), 8 deletions(-)
diff --git a/mm/secretmem.c b/mm/secretmem.c
index 206ed6b40c1d..40573b045c96 100644
--- a/mm/secretmem.c
+++ b/mm/secretmem.c
@@ -47,30 +47,41 @@ bool secretmem_active(void)
return !!atomic_read(&secretmem_users);
}
+struct secretmem_state {
+ struct rw_semaphore rw_sem;
+};
+
static vm_fault_t secretmem_fault(struct vm_fault *vmf)
{
struct address_space *mapping = vmf->vma->vm_file->f_mapping;
struct inode *inode = file_inode(vmf->vma->vm_file);
+ struct secretmem_state *state = inode->i_private;
pgoff_t offset = vmf->pgoff;
gfp_t gfp = vmf->gfp_mask;
unsigned long addr;
struct page *page;
+ vm_fault_t ret;
int err;
if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
return vmf_error(-EINVAL);
+ down_read(&state->rw_sem);
+
retry:
page = find_lock_page(mapping, offset);
if (!page) {
page = alloc_page(gfp | __GFP_ZERO);
- if (!page)
- return VM_FAULT_OOM;
+ if (!page) {
+ ret = VM_FAULT_OOM;
+ goto out;
+ }
err = set_direct_map_invalid_noflush(page);
if (err) {
put_page(page);
- return vmf_error(err);
+ ret = vmf_error(err);
+ goto out;
}
__SetPageUptodate(page);
@@ -86,7 +97,8 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf)
if (err == -EEXIST)
goto retry;
- return vmf_error(err);
+ ret = vmf_error(err);
+ goto out;
}
addr = (unsigned long)page_address(page);
@@ -94,7 +106,11 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf)
}
vmf->page = page;
- return VM_FAULT_LOCKED;
+ ret = VM_FAULT_LOCKED;
+
+out:
+ up_read(&state->rw_sem);
+ return ret;
}
static const struct vm_operations_struct secretmem_vm_ops = {
@@ -163,11 +179,17 @@ static int secretmem_setattr(struct user_namespace *mnt_userns,
{
struct inode *inode = d_inode(dentry);
unsigned int ia_valid = iattr->ia_valid;
+ struct secretmem_state *state = inode->i_private;
+ int ret;
+ down_write(&state->rw_sem);
if ((ia_valid & ATTR_SIZE) && inode->i_size)
- return -EINVAL;
+ ret = -EINVAL;
+ else
+ ret = simple_setattr(mnt_userns, dentry, iattr);
+ up_write(&state->rw_sem);
- return simple_setattr(mnt_userns, dentry, iattr);
+ return ret;
}
static const struct inode_operations secretmem_iops = {
@@ -179,22 +201,30 @@ static struct vfsmount *secretmem_mnt;
static struct file *secretmem_file_create(unsigned long flags)
{
struct file *file = ERR_PTR(-ENOMEM);
+ struct secretmem_state *state;
struct inode *inode;
inode = alloc_anon_inode(secretmem_mnt->mnt_sb);
if (IS_ERR(inode))
return ERR_CAST(inode);
+ state = kzalloc(sizeof(*state), GFP_KERNEL);
+ if (!state)
+ goto err_free_inode;
+
file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
O_RDWR, &secretmem_fops);
if (IS_ERR(file))
- goto err_free_inode;
+ goto err_free_state;
mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
mapping_set_unevictable(inode->i_mapping);
+ init_rwsem(&state->rw_sem);
+
inode->i_op = &secretmem_iops;
inode->i_mapping->a_ops = &secretmem_aops;
+ inode->i_private = state;
/* pretend we are a normal file with zero size */
inode->i_mode |= S_IFREG;
@@ -202,6 +232,8 @@ static struct file *secretmem_file_create(unsigned long flags)
return file;
+err_free_state:
+ kfree(state);
err_free_inode:
iput(inode);
return file;
base-commit: 03c765b0e3b4cb5063276b086c76f7a612856a9a
--
2.34.1
> > The following commit tried to fix a similar bug, but it wasn't enough:
> >
> > commit f9b141f93659e09a52e28791ccbaf69c273b8e92
> > Author: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
> > Date: Thu Apr 14 19:13:31 2022 -0700
> >
> > mm/secretmem: fix panic when growing a memfd_secret
> >
> >
> > Here's a simplified reproducer. Note, for memfd_secret to be supported, the
> > kernel config must contain CONFIG_SECRETMEM=y and the kernel command line must
> > contain secretmem.enable=1.
> >
> > #include <pthread.h>
> > #include <setjmp.h>
> > #include <signal.h>
> > #include <sys/mman.h>
> > #include <sys/syscall.h>
> > #include <unistd.h>
> >
> > static volatile int fd;
> > static jmp_buf jump_buf;
> >
> > static void *truncate_thread(void *arg)
> > {
> > for (;;)
> > ftruncate(fd, 1000);
> > }
> >
> > static void handle_sigbus(int sig)
> > {
> > longjmp(jump_buf, 1);
> > }
> >
> > int main(void)
> > {
> > struct sigaction act = {
> > .sa_handler = handle_sigbus,
> > .sa_flags = SA_NODEFER,
> > };
> > pthread_t t;
> > void *addr;
> >
> > sigaction(SIGBUS, &act, NULL);
> >
> > pthread_create(&t, NULL, truncate_thread, NULL);
> > for (;;) {
> > fd = syscall(__NR_memfd_secret, 0);
> > addr = mmap(NULL, 8192, PROT_WRITE, MAP_SHARED, fd, 0);
> > if (setjmp(jump_buf) == 0)
> > *(unsigned int *)addr = 0;
> > munmap(addr, 8192);
> > close(fd);
> > }
> > }
--
Sincerely yours,
Mike.