On Tue, May 05, 2020 at 05:31:52PM +0200, Mickaël Salaün wrote: > This new MAY_EXECMOUNT flag enables to check if the underlying mount > point of an inode is marked as executable. This is useful to implement > a security policy taking advantage of the noexec mount option. > > This flag is set according to path_noexec(), which checks if a mount > point is mounted with MNT_NOEXEC or if the underlying superblock is > SB_I_NOEXEC. > > Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx> > Reviewed-by: Philippe Trébuchet <philippe.trebuchet@xxxxxxxxxxx> > Reviewed-by: Thibaut Sautereau <thibaut.sautereau@xxxxxxxxxxx> > Cc: Aleksa Sarai <cyphar@xxxxxxxxxx> > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > --- > fs/namei.c | 2 ++ > include/linux/fs.h | 2 ++ > 2 files changed, 4 insertions(+) > > diff --git a/fs/namei.c b/fs/namei.c > index a320371899cf..33b6d372e74a 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -2849,6 +2849,8 @@ static int may_open(const struct path *path, int acc_mode, int flag) > break; > } > > + /* Pass the mount point executability. */ > + acc_mode |= path_noexec(path) ? 0 : MAY_EXECMOUNT; > error = inode_permission(inode, MAY_OPEN | acc_mode); > if (error) > return error; > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 313c934de9ee..79435fca6c3e 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -103,6 +103,8 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset, > #define MAY_NOT_BLOCK 0x00000080 > /* the inode is opened with O_MAYEXEC */ > #define MAY_OPENEXEC 0x00000100 > +/* the mount point is marked as executable */ > +#define MAY_EXECMOUNT 0x00000200 > > /* > * flags in file.f_mode. Note that FMODE_READ and FMODE_WRITE must correspond I find this name unintuitive, but I cannot think of anything better, since I think my problem is that "MAY" doesn't map to the language I want to use to describe what this flag is indicating. Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -- Kees Cook
