linux-kernel - [RFC][PATCH] mm: Split locks in remap_file

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-Id: <20241018144710.3800385-1-roberto.sassu@huaweicloud.com>
Date: Fri, 18 Oct 2024 16:47:10 +0200
From: Roberto Sassu <roberto.sassu@...weicloud.com>
To: akpm@...ux-foundation.org,
	Liam.Howlett@...cle.com,
	lorenzo.stoakes@...cle.com,
	vbabka@...e.cz,
	jannh@...gle.com
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	ebpqwerty472123@...il.com,
	paul@...l-moore.com,
	zohar@...ux.ibm.com,
	dmitry.kasatkin@...il.com,
	eric.snowberg@...cle.com,
	jmorris@...ei.org,
	serge@...lyn.com,
	linux-integrity@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	bpf@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	stable@...r.kernel.org,
	syzbot+91ae49e1c1a2634d20c0@...kaller.appspotmail.com,
	Roberto Sassu <roberto.sassu@...wei.com>
Subject: [RFC][PATCH] mm: Split locks in remap_file_pages()

From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>

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 and retrieves the VMA
and the file associated, and calculate the 'prot' and 'flags' variable; 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 taking the write lock, call
security_mmap_file(), and solve the lock inversion issue.

Cc: stable@...r.kernel.org
Fixes: ea7e2d5e49c0 ("mm: call the security_mmap_file() LSM hook in remap_file_pages()")
Reported-by: syzbot+91ae49e1c1a2634d20c0@...kaller.appspotmail.com
Closes: https://lore.kernel.org/linux-security-module/66f7b10e.050a0220.46d20.0036.GAE@google.com/
Reviewed-by: Roberto Sassu <roberto.sassu@...wei.com> (Calculate prot and flags earlier)
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 mm/mmap.c | 62 ++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 45 insertions(+), 17 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 9c0fb43064b5..762944427e03 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1640,6 +1640,7 @@ 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);
@@ -1656,12 +1657,53 @@ 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;
+
+	vma = vma_lookup(mm, start);
+
+	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);
+
+	ret = security_mmap_file(file, prot, flags);
+	if (ret) {
+		fput(file);
+		return ret;
+	}
+
+	ret = -EINVAL;
+
+	if (mmap_write_lock_killable(mm)) {
+		fput(file);
 		return -EINTR;
+	}
 
 	vma = vma_lookup(mm, start);
 
-	if (!vma || !(vma->vm_flags & VM_SHARED))
+	if (!vma)
+		goto out;
+
+	if (vma->vm_flags != vm_flags)
+		goto out;
+
+	if (vma->vm_file != file)
 		goto out;
 
 	if (start + size > vma->vm_end) {
@@ -1689,25 +1731,11 @@ 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, 0, 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))
-- 
2.34.1