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vfs: fix do_last() regression

This commit is contained in:
Salvatore Bonaccorso 2020-02-01 21:05:22 +01:00
parent d3e1b6996d
commit 241912ed84
3 changed files with 59 additions and 0 deletions
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1
debian/changelog vendored
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@ -3,6 +3,7 @@ linux (4.19.98-1+deb10u1) UNRELEASED; urgency=medium
* [x86] KVM: nVMX: Don't emulate instructions in guest mode (CVE-2020-2732)
* do_last(): fetch directory ->i_mode and ->i_uid before it's too late
(CVE-2020-8428)
* vfs: fix do_last() regression
-- Salvatore Bonaccorso <carnil@debian.org> Sun, 26 Apr 2020 20:32:58 +0200

57
debian/patches/bugfix/all/vfs-fix-do_last-regression.patch vendored Normal file
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@ -0,0 +1,57 @@
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Sat, 1 Feb 2020 16:26:45 +0000
Subject: vfs: fix do_last() regression
Origin: https://git.kernel.org/linus/6404674acd596de41fd3ad5f267b4525494a891a
Brown paperbag time: fetching ->i_uid/->i_mode really should've been
done from nd->inode. I even suggested that, but the reason for that has
slipped through the cracks and I went for dir->d_inode instead - made
for more "obvious" patch.
Analysis:
- at the entry into do_last() and all the way to step_into(): dir (aka
nd->path.dentry) is known not to have been freed; so's nd->inode and
it's equal to dir->d_inode unless we are already doomed to -ECHILD.
inode of the file to get opened is not known.
- after step_into(): inode of the file to get opened is known; dir
might be pointing to freed memory/be negative/etc.
- at the call of may_create_in_sticky(): guaranteed to be out of RCU
mode; inode of the file to get opened is known and pinned; dir might
be garbage.
The last was the reason for the original patch. Except that at the
do_last() entry we can be in RCU mode and it is possible that
nd->path.dentry->d_inode has already changed under us.
In that case we are going to fail with -ECHILD, but we need to be
careful; nd->inode is pointing to valid struct inode and it's the same
as nd->path.dentry->d_inode in "won't fail with -ECHILD" case, so we
should use that.
Reported-by: "Rantala, Tommi T. (Nokia - FI/Espoo)" <tommi.t.rantala@nokia.com>
Reported-by: syzbot+190005201ced78a74ad6@syzkaller.appspotmail.com
Wearing-brown-paperbag: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@kernel.org
Fixes: d0cb50185ae9 ("do_last(): fetch directory ->i_mode and ->i_uid before it's too late")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
fs/namei.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3259,8 +3259,8 @@ static int do_last(struct nameidata *nd,
struct file *file, const struct open_flags *op)
{
struct dentry *dir = nd->path.dentry;
- kuid_t dir_uid = dir->d_inode->i_uid;
- umode_t dir_mode = dir->d_inode->i_mode;
+ kuid_t dir_uid = nd->inode->i_uid;
+ umode_t dir_mode = nd->inode->i_mode;
int open_flag = op->open_flag;
bool will_truncate = (open_flag & O_TRUNC) != 0;
bool got_write = false;

1
debian/patches/series vendored
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@ -306,6 +306,7 @@ bugfix/all/wimax-i2400-fix-memory-leak.patch
bugfix/all/wimax-i2400-fix-memory-leak-in-i2400m_op_rfkill_sw_toggle.patch
bugfix/x86/KVM-nVMX-Don-t-emulate-instructions-in-guest-mode.patch
bugfix/all/do_last-fetch-directory-i_mode-and-i_uid-before-it-s.patch
bugfix/all/vfs-fix-do_last-regression.patch
# Backported change to provide boot-time entropy
bugfix/all/random-try-to-actively-add-entropy-rather-than-passi.patch