fs: Fix rw_hint validation

Reject values that are valid rw_hints after truncation but not before
truncation by passing an untruncated value to rw_hint_valid().

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kanchan Joshi <joshi.k@samsung.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 5657cb0797c4 ("fs/fcntl: use copy_to/from_user() for u64 types")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20240202203926.2478590-2-bvanassche@acm.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/fcntl.c b/fs/fcntl.c
index c80a6acad742fb027a4a990f63ef05d0678736d7..3ff707bf2743a6fb5b0c2064cc510ab984230641 100644 (file)
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -268,7 +268,7 @@ static int f_getowner_uids(struct file *filp, unsigned long arg)
 }
 #endif
 
-static bool rw_hint_valid(enum rw_hint hint)
+static bool rw_hint_valid(u64 hint)
 {
        switch (hint) {
        case RWH_WRITE_LIFE_NOT_SET:
@@ -288,19 +288,17 @@ static long fcntl_rw_hint(struct file *file, unsigned int cmd,
 {
        struct inode *inode = file_inode(file);
        u64 __user *argp = (u64 __user *)arg;
-       enum rw_hint hint;
-       u64 h;
+       u64 hint;
 
        switch (cmd) {
        case F_GET_RW_HINT:
-               h = inode->i_write_hint;
-               if (copy_to_user(argp, &h, sizeof(*argp)))
+               hint = inode->i_write_hint;
+               if (copy_to_user(argp, &hint, sizeof(*argp)))
                        return -EFAULT;
                return 0;
        case F_SET_RW_HINT:
-               if (copy_from_user(&h, argp, sizeof(h)))
+               if (copy_from_user(&hint, argp, sizeof(hint)))
                        return -EFAULT;
-               hint = (enum rw_hint) h;
                if (!rw_hint_valid(hint))
                        return -EINVAL;