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do_last(): fetch directory ->i_mode and ->i_uid before it's too late (CVE-2020-8428)

This commit is contained in:
Salvatore Bonaccorso 2020-01-29 06:52:40 +01:00
parent a688ee48fb
commit d3e1b6996d
3 changed files with 73 additions and 0 deletions
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2
debian/changelog vendored
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@ -1,6 +1,8 @@
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)
-- Salvatore Bonaccorso <carnil@debian.org> Sun, 26 Apr 2020 20:32:58 +0200

70
debian/patches/bugfix/all/do_last-fetch-directory-i_mode-and-i_uid-before-it-s.patch vendored Normal file
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@ -0,0 +1,70 @@
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Sun, 26 Jan 2020 09:29:34 -0500
Subject: do_last(): fetch directory ->i_mode and ->i_uid before it's too late
Origin: https://git.kernel.org/linus/d0cb50185ae942b03c4327be322055d622dc79f6
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2020-8428
may_create_in_sticky() call is done when we already have dropped the
reference to dir.
Fixes: 30aba6656f61e (namei: allow restricted O_CREAT of FIFOs and regular files)
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[Salvatore Bonaccorso: Backport to 4.19.98 for context changes]
---
fs/namei.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1009,7 +1009,8 @@ static int may_linkat(struct path *link)
* may_create_in_sticky - Check whether an O_CREAT open in a sticky directory
* should be allowed, or not, on files that already
* exist.
- * @dir: the sticky parent directory
+ * @dir_mode: mode bits of directory
+ * @dir_uid: owner of directory
* @inode: the inode of the file to open
*
* Block an O_CREAT open of a FIFO (or a regular file) when:
@@ -1025,18 +1026,18 @@ static int may_linkat(struct path *link)
*
* Returns 0 if the open is allowed, -ve on error.
*/
-static int may_create_in_sticky(struct dentry * const dir,
+static int may_create_in_sticky(umode_t dir_mode, kuid_t dir_uid,
struct inode * const inode)
{
if ((!sysctl_protected_fifos && S_ISFIFO(inode->i_mode)) ||
(!sysctl_protected_regular && S_ISREG(inode->i_mode)) ||
- likely(!(dir->d_inode->i_mode & S_ISVTX)) ||
- uid_eq(inode->i_uid, dir->d_inode->i_uid) ||
+ likely(!(dir_mode & S_ISVTX)) ||
+ uid_eq(inode->i_uid, dir_uid) ||
uid_eq(current_fsuid(), inode->i_uid))
return 0;
- if (likely(dir->d_inode->i_mode & 0002) ||
- (dir->d_inode->i_mode & 0020 &&
+ if (likely(dir_mode & 0002) ||
+ (dir_mode & 0020 &&
((sysctl_protected_fifos >= 2 && S_ISFIFO(inode->i_mode)) ||
(sysctl_protected_regular >= 2 && S_ISREG(inode->i_mode))))) {
return -EACCES;
@@ -3258,6 +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;
int open_flag = op->open_flag;
bool will_truncate = (open_flag & O_TRUNC) != 0;
bool got_write = false;
@@ -3393,7 +3396,7 @@ finish_open:
error = -EISDIR;
if (d_is_dir(nd->path.dentry))
goto out;
- error = may_create_in_sticky(dir,
+ error = may_create_in_sticky(dir_mode, dir_uid,
d_backing_inode(nd->path.dentry));
if (unlikely(error))
goto out;

1
debian/patches/series vendored
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@ -305,6 +305,7 @@ bugfix/all/libertas-fix-two-buffer-overflows-at-parsing-bss-descriptor.patch
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
# Backported change to provide boot-time entropy
bugfix/all/random-try-to-actively-add-entropy-rather-than-passi.patch