From: "Kirill A. Shutemov" kirill.shutemov@linux.intel.com

commit 58a039e679fe72bd0efa8b2abe669a7914bb4429 upstream.

Commit ea7e2d5e49c0 ("mm: call the security_mmap_file() LSM hook in remap_file_pages()") fixed a security issue, it added an LSM check when trying to remap file pages, so that LSMs have the opportunity to evaluate such action like for other memory operations such as mmap() and mprotect().

However, that commit called security_mmap_file() inside the mmap_lock lock, while the other calls do it before taking the lock, after commit 8b3ec6814c83 ("take security_mmap_file() outside of ->mmap_sem").

This caused lock inversion issue with IMA which was taking the mmap_lock and i_mutex lock in the opposite way when the remap_file_pages() system call was called.

Solve the issue by splitting the critical region in remap_file_pages() in two regions: the first takes a read lock of mmap_lock, retrieves the VMA and the file descriptor associated, and calculates the 'prot' and 'flags' variables; the second takes a write lock on mmap_lock, checks that the VMA flags and the VMA file descriptor are the same as the ones obtained in the first critical region (otherwise the system call fails), and calls do_mmap().

In between, after releasing the read lock and before taking the write lock, call security_mmap_file(), and solve the lock inversion issue.

Link: https://lkml.kernel.org/r/20241018161415.3845146-1-roberto.sassu@huaweicloud... Fixes: ea7e2d5e49c0 ("mm: call the security_mmap_file() LSM hook in remap_file_pages()") Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Signed-off-by: Roberto Sassu roberto.sassu@huawei.com Reported-by: syzbot+1cd571a672400ef3a930@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-security-module/66f7b10e.050a0220.46d20.0036.G... Tested-by: Roberto Sassu roberto.sassu@huawei.com Reviewed-by: Roberto Sassu roberto.sassu@huawei.com Reviewed-by: Jann Horn jannh@google.com Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com Reviewed-by: Liam R. Howlett Liam.Howlett@Oracle.com Reviewed-by: Paul Moore paul@paul-moore.com Tested-by: syzbot+1cd571a672400ef3a930@syzkaller.appspotmail.com Cc: Jarkko Sakkinen jarkko@kernel.org Cc: Dmitry Kasatkin dmitry.kasatkin@gmail.com Cc: Eric Snowberg eric.snowberg@oracle.com Cc: James Morris jmorris@namei.org Cc: Mimi Zohar zohar@linux.ibm.com Cc: "Serge E. Hallyn" serge@hallyn.com Cc: Shu Han ebpqwerty472123@gmail.com Cc: Vlastimil Babka vbabka@suse.cz Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Alexey Panov apanov@astralinux.ru --- Tested with the syzkaller reproducers for https://syzkaller.appspot.com/bug?extid=1cd571a672400ef3a930 https://syzkaller.appspot.com/bug?extid=b02bbe0ff80a09a08c1b: the issue triggers on vanilla v6.1.y and no longer reproduces with this patch applied. mm/mmap.c | 69 +++++++++++++++++++++++++++++++++++++++++-------------- 1 file changed, 52 insertions(+), 17 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c index f93526b3df0c..5672d22be7e7 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2974,6 +2974,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size, unsigned long populate = 0; unsigned long ret = -EINVAL; struct file *file; + vm_flags_t vm_flags;

pr_warn_once("%s (%d) uses deprecated remap_file_pages() syscall. See Documentation/mm/remap_file_pages.rst.\n", current->comm, current->pid); @@ -2990,12 +2991,60 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size, if (pgoff + (size >> PAGE_SHIFT) < pgoff) return ret;

- if (mmap_write_lock_killable(mm)) + if (mmap_read_lock_killable(mm)) return -EINTR;

+ /* + * Look up VMA under read lock first so we can perform the security + * without holding locks (which can be problematic). We reacquire a + * write lock later and check nothing changed underneath us. + */ vma = vma_lookup(mm, start);

- if (!vma || !(vma->vm_flags & VM_SHARED)) + if (!vma || !(vma->vm_flags & VM_SHARED)) { + mmap_read_unlock(mm); + return -EINVAL; + } + + prot |= vma->vm_flags & VM_READ ? PROT_READ : 0; + prot |= vma->vm_flags & VM_WRITE ? PROT_WRITE : 0; + prot |= vma->vm_flags & VM_EXEC ? PROT_EXEC : 0; + + flags &= MAP_NONBLOCK; + flags |= MAP_SHARED | MAP_FIXED | MAP_POPULATE; + if (vma->vm_flags & VM_LOCKED) + flags |= MAP_LOCKED; + + /* Save vm_flags used to calculate prot and flags, and recheck later. */ + vm_flags = vma->vm_flags; + file = get_file(vma->vm_file); + + mmap_read_unlock(mm); + + /* Call outside mmap_lock to be consistent with other callers. */ + ret = security_mmap_file(file, prot, flags); + if (ret) { + fput(file); + return ret; + } + + ret = -EINVAL; + + /* OK security check passed, take write lock + let it rip. */ + if (mmap_write_lock_killable(mm)) { + fput(file); + return -EINTR; + } + + vma = vma_lookup(mm, start); + + if (!vma) + goto out; + + /* Make sure things didn't change under us. */ + if (vma->vm_flags != vm_flags) + goto out; + if (vma->vm_file != file) goto out;

if (start + size > vma->vm_end) { @@ -3023,25 +3072,11 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size, goto out; }

- prot |= vma->vm_flags & VM_READ ? PROT_READ : 0; - prot |= vma->vm_flags & VM_WRITE ? PROT_WRITE : 0; - prot |= vma->vm_flags & VM_EXEC ? PROT_EXEC : 0; - - flags &= MAP_NONBLOCK; - flags |= MAP_SHARED | MAP_FIXED | MAP_POPULATE; - if (vma->vm_flags & VM_LOCKED) - flags |= MAP_LOCKED; - - file = get_file(vma->vm_file); - ret = security_mmap_file(vma->vm_file, prot, flags); - if (ret) - goto out_fput; ret = do_mmap(vma->vm_file, start, size, prot, flags, pgoff, &populate, NULL); -out_fput: - fput(file); out: mmap_write_unlock(mm); + fput(file); if (populate) mm_populate(ret, populate); if (!IS_ERR_VALUE(ret))