49 lines
1.8 KiB
Diff
49 lines
1.8 KiB
Diff
From: Piotr Krysiuk <piotras@gmail.com>
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Date: Mon, 27 Apr 2020 11:34:12 +0100
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Subject: fs/namespace.c: fix mountpoint reference counter race
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Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f511dc75d22e0c000fc70b54f670c2c17f5fba9a
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Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2020-12114
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A race condition between threads updating mountpoint reference counter
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affects longterm releases 4.4.220, 4.9.220, 4.14.177 and 4.19.118.
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The mountpoint reference counter corruption may occur when:
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* one thread increments m_count member of struct mountpoint
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[under namespace_sem, but not holding mount_lock]
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pivot_root()
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* another thread simultaneously decrements the same m_count
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[under mount_lock, but not holding namespace_sem]
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put_mountpoint()
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unhash_mnt()
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umount_mnt()
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mntput_no_expire()
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To fix this race condition, grab mount_lock before updating m_count in
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pivot_root().
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Reference: CVE-2020-12114
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Cc: Al Viro <viro@zeniv.linux.org.uk>
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Signed-off-by: Piotr Krysiuk <piotras@gmail.com>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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fs/namespace.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/fs/namespace.c b/fs/namespace.c
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index 1fce41ba3535..741f40cd955e 100644
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--- a/fs/namespace.c
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+++ b/fs/namespace.c
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@@ -3142,8 +3142,8 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
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/* make certain new is below the root */
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if (!is_path_reachable(new_mnt, new.dentry, &root))
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goto out4;
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- root_mp->m_count++; /* pin it so it won't go away */
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lock_mount_hash();
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+ root_mp->m_count++; /* pin it so it won't go away */
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detach_mnt(new_mnt, &parent_path);
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detach_mnt(root_mnt, &root_parent);
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if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
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--
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2.27.0.rc0
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