vfs: fix do_last() regression
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@ -2,6 +2,7 @@ linux (4.19.98-2) UNRELEASED; urgency=medium
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* do_last(): fetch directory ->i_mode and ->i_uid before it's too late
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* do_last(): fetch directory ->i_mode and ->i_uid before it's too late
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(CVE-2020-8428)
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(CVE-2020-8428)
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* vfs: fix do_last() regression
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-- Salvatore Bonaccorso <carnil@debian.org> Wed, 29 Jan 2020 06:52:57 +0100
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-- Salvatore Bonaccorso <carnil@debian.org> Wed, 29 Jan 2020 06:52:57 +0100
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@ -0,0 +1,57 @@
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From: Al Viro <viro@zeniv.linux.org.uk>
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Date: Sat, 1 Feb 2020 16:26:45 +0000
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Subject: vfs: fix do_last() regression
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Origin: https://git.kernel.org/linus/6404674acd596de41fd3ad5f267b4525494a891a
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Brown paperbag time: fetching ->i_uid/->i_mode really should've been
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done from nd->inode. I even suggested that, but the reason for that has
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slipped through the cracks and I went for dir->d_inode instead - made
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for more "obvious" patch.
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Analysis:
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- at the entry into do_last() and all the way to step_into(): dir (aka
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nd->path.dentry) is known not to have been freed; so's nd->inode and
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it's equal to dir->d_inode unless we are already doomed to -ECHILD.
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inode of the file to get opened is not known.
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- after step_into(): inode of the file to get opened is known; dir
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might be pointing to freed memory/be negative/etc.
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- at the call of may_create_in_sticky(): guaranteed to be out of RCU
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mode; inode of the file to get opened is known and pinned; dir might
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be garbage.
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The last was the reason for the original patch. Except that at the
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do_last() entry we can be in RCU mode and it is possible that
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nd->path.dentry->d_inode has already changed under us.
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In that case we are going to fail with -ECHILD, but we need to be
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careful; nd->inode is pointing to valid struct inode and it's the same
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as nd->path.dentry->d_inode in "won't fail with -ECHILD" case, so we
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should use that.
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Reported-by: "Rantala, Tommi T. (Nokia - FI/Espoo)" <tommi.t.rantala@nokia.com>
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Reported-by: syzbot+190005201ced78a74ad6@syzkaller.appspotmail.com
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Wearing-brown-paperbag: Al Viro <viro@zeniv.linux.org.uk>
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Cc: stable@kernel.org
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Fixes: d0cb50185ae9 ("do_last(): fetch directory ->i_mode and ->i_uid before it's too late")
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Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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fs/namei.c | 4 ++--
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1 file changed, 2 insertions(+), 2 deletions(-)
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--- a/fs/namei.c
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+++ b/fs/namei.c
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@@ -3259,8 +3259,8 @@ static int do_last(struct nameidata *nd,
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struct file *file, const struct open_flags *op)
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{
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struct dentry *dir = nd->path.dentry;
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- kuid_t dir_uid = dir->d_inode->i_uid;
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- umode_t dir_mode = dir->d_inode->i_mode;
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+ kuid_t dir_uid = nd->inode->i_uid;
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+ umode_t dir_mode = nd->inode->i_mode;
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int open_flag = op->open_flag;
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bool will_truncate = (open_flag & O_TRUNC) != 0;
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bool got_write = false;
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@ -305,6 +305,7 @@ bugfix/all/libertas-fix-two-buffer-overflows-at-parsing-bss-descriptor.patch
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bugfix/all/wimax-i2400-fix-memory-leak.patch
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bugfix/all/wimax-i2400-fix-memory-leak.patch
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bugfix/all/wimax-i2400-fix-memory-leak-in-i2400m_op_rfkill_sw_toggle.patch
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bugfix/all/wimax-i2400-fix-memory-leak-in-i2400m_op_rfkill_sw_toggle.patch
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bugfix/all/do_last-fetch-directory-i_mode-and-i_uid-before-it-s.patch
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bugfix/all/do_last-fetch-directory-i_mode-and-i_uid-before-it-s.patch
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bugfix/all/vfs-fix-do_last-regression.patch
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# Backported change to provide boot-time entropy
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# Backported change to provide boot-time entropy
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bugfix/all/random-try-to-actively-add-entropy-rather-than-passi.patch
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bugfix/all/random-try-to-actively-add-entropy-rather-than-passi.patch
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