The patch titled
Subject: mm/mmap.c: clear file privilege bits when mmap writing
has been added to the -mm tree. Its filename is
fs-clear-file-privilege-bits-when-mmap-writing.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/fs-clear-file-privilege-bits-when-mmap-writing.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/fs-clear-file-privilege-bits-when-mmap-writing.patch
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The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Kees Cook <[email protected]>
Subject: mm/mmap.c: clear file privilege bits when mmap writing
Normally, when a user can modify a file that has setuid or setgid bits,
those bits are cleared when they are not the file owner or a member of the
group. This is enforced when using write and truncate but not when
writing to a shared mmap on the file. This could allow the file writer to
gain privileges by changing a binary without losing the setuid/setgid/caps
bits.
Changing the bits requires holding inode->i_mutex, so it cannot be done
during the page fault (due to mmap_sem being held during the fault).
Instead, clear the bits if PROT_WRITE is being used at mmap time.
Signed-off-by: Kees Cook <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Willy Tarreau <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Chen Gang <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
mm/mmap.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff -puN mm/mmap.c~fs-clear-file-privilege-bits-when-mmap-writing mm/mmap.c
--- a/mm/mmap.c~fs-clear-file-privilege-bits-when-mmap-writing
+++ a/mm/mmap.c
@@ -1352,6 +1352,17 @@ unsigned long do_mmap(struct file *file,
if (locks_verify_locked(file))
return -EAGAIN;
+ /*
+ * If we must remove privs, we do it here since
+ * doing it during page COW is expensive and
+ * cannot hold inode->i_mutex.
+ */
+ if (prot & PROT_WRITE && !IS_NOSEC(inode)) {
+ mutex_lock(&inode->i_mutex);
+ file_remove_privs(file);
+ mutex_unlock(&inode->i_mutex);
+ }
+
vm_flags |= VM_SHARED | VM_MAYSHARE;
if (!(file->f_mode & FMODE_WRITE))
vm_flags &= ~(VM_MAYWRITE | VM_SHARED);
_
Patches currently in -mm which might be from [email protected] are
fs-clear-file-privilege-bits-when-mmap-writing.patch
sysctl-enable-strict-writes.patch
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