On Mon, Feb 28, 2022 at 10:59:35PM +0100, Mickaël Salaün wrote: > From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> > > While transitionning to ACC_MODE() with commit 5300990c0370 ("Sanitize > f_flags helpers") and then fixing it with commit 6d125529c6cb ("Fix > ACC_MODE() for real"), we lost an open flags consistency check. Opening > a file with O_WRONLY | O_RDWR leads to an f_flags containing MAY_READ | > MAY_WRITE (thanks to the ACC_MODE() helper) and an empty f_mode. > Indeed, the OPEN_FMODE() helper transforms 3 (an incorrect value) to 0. > > Fortunately, vfs_read() and vfs_write() both check for FMODE_READ, or > respectively FMODE_WRITE, and return an EBADF error if it is absent. > Before commit 5300990c0370 ("Sanitize f_flags helpers"), opening a file > with O_WRONLY | O_RDWR returned an EINVAL error. Let's restore this safe > behavior. That specific part seems a bit risky at first glance. Given that the patch referenced is from 2009 this means we've been allowing O_WRONLY | O_RDWR to succeed for almost 13 years now. > > To make it consistent with ACC_MODE(), this patch also changes > OPEN_FMODE() to return FMODE_READ | FMODE_WRITE for O_WRONLY | O_RDWR. > This may help protect from potential spurious issues. > > This issue could result in inconsistencies with AppArmor, Landlock and > SELinux, but the VFS checks would still forbid read and write accesses. > Tomoyo uses the ACC_MODE() transformation which is correct, and Smack > doesn't check the file mode. Filesystems using OPEN_FMODE() should also > be protected by the VFS checks. > > Fixes: 5300990c0370 ("Sanitize f_flags helpers") > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > Cc: Casey Schaufler <casey@xxxxxxxxxxxxxxxx> > Cc: Darrick J. Wong <djwong@xxxxxxxxxx> > Cc: Eric Paris <eparis@xxxxxxxxxxxxxx> > Cc: John Johansen <john.johansen@xxxxxxxxxxxxx> > Cc: Kentaro Takeda <takedakn@xxxxxxxxxxxxx> > Cc: Miklos Szeredi <miklos@xxxxxxxxxx> > Cc: Paul Moore <paul@xxxxxxxxxxxxxx> > Cc: Stephen Smalley <stephen.smalley.work@xxxxxxxxx> > Cc: Steve French <sfrench@xxxxxxxxx> > Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> > Link: https://lore.kernel.org/r/20220228215935.748017-1-mic@xxxxxxxxxxx > --- > fs/file_table.c | 3 +++ > include/linux/fs.h | 5 +++-- > 2 files changed, 6 insertions(+), 2 deletions(-) > > diff --git a/fs/file_table.c b/fs/file_table.c > index 7d2e692b66a9..b936f69525d0 100644 > --- a/fs/file_table.c > +++ b/fs/file_table.c > @@ -135,6 +135,9 @@ static struct file *__alloc_file(int flags, const struct cred *cred) > struct file *f; > int error; > > + if ((flags & O_ACCMODE) == O_ACCMODE) > + return ERR_PTR(-EINVAL); > + > f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL); > if (unlikely(!f)) > return ERR_PTR(-ENOMEM); > diff --git a/include/linux/fs.h b/include/linux/fs.h > index e2d892b201b0..83bc5aaf1c41 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -3527,8 +3527,9 @@ int __init list_bdev_fs_names(char *buf, size_t size); > #define __FMODE_NONOTIFY ((__force int) FMODE_NONOTIFY) > > #define ACC_MODE(x) ("\004\002\006\006"[(x)&O_ACCMODE]) > -#define OPEN_FMODE(flag) ((__force fmode_t)(((flag + 1) & O_ACCMODE) | \ > - (flag & __FMODE_NONOTIFY))) > +#define OPEN_FMODE(flag) ((__force fmode_t)( \ > + (((flag + 1) & O_ACCMODE) ?: O_ACCMODE) | \ > + (flag & __FMODE_NONOTIFY))) > > static inline bool is_sxid(umode_t mode) > { > > base-commit: 7e57714cd0ad2d5bb90e50b5096a0e671dec1ef3 > -- > 2.35.1 >