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authorAl Viro <viro@zeniv.linux.org.uk>2020-02-01 16:26:45 +0000
committerLinus Torvalds <torvalds@linux-foundation.org>2020-02-01 10:36:49 -0800
commit6404674acd596de41fd3ad5f267b4525494a891a (patch)
treed569cd4f4f86f53539334506ef38486aca6919ba /fs/namei.c
parent14cd0bd04907df79b36a31e55f18768172230987 (diff)
downloadblackbird-op-linux-6404674acd596de41fd3ad5f267b4525494a891a.tar.gz
blackbird-op-linux-6404674acd596de41fd3ad5f267b4525494a891a.zip
vfs: fix do_last() regression
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>
Diffstat (limited to 'fs/namei.c')
-rw-r--r--fs/namei.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/namei.c b/fs/namei.c
index 4167109297e0..db6565c99825 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3333,8 +3333,8 @@ 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;
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