[PATCH] Fix wrong max check in bch2_opt_validate

[Piotr Zalewski]

Use opt->max-1 in bch2_opt_validate when option type is BCH_OPT_STR. When
option type is BCH_OPT_STR, real option's max is one less than the max
value stored in option structure.

Reported-by: syzbot+bee87a0c3291c06aa8c6@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=bee87a0c3291c06aa8c6
Fixes: 63c4b2545382 ("bcachefs: Better superblock opt validation")
Signed-off-by: Piotr Zalewski <pZ010001011111@xxxxxxxxx>
---
 fs/bcachefs/opts.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/bcachefs/opts.c b/fs/bcachefs/opts.c
index 83f55cf99d46..bffcbe6a6fd0 100644
--- a/fs/bcachefs/opts.c
+++ b/fs/bcachefs/opts.c
@@ -290,6 +290,8 @@ static int bch2_mount_opt_lookup(const char *name)
 
 int bch2_opt_validate(const struct bch_option *opt, u64 v, struct printbuf *err)
 {
+	const u64 opt_max = opt->type == BCH_OPT_STR ? opt->max - 1 : opt->max;
+
 	if (v < opt->min) {
 		if (err)
 			prt_printf(err, "%s: too small (min %llu)",
@@ -297,10 +299,10 @@ int bch2_opt_validate(const struct bch_option *opt, u64 v, struct printbuf *err)
 		return -BCH_ERR_ERANGE_option_too_small;
 	}
 
-	if (opt->max && v >= opt->max) {
+	if (opt->max && v >= opt_max) {
 		if (err)
 			prt_printf(err, "%s: too big (max %llu)",
-			       opt->attr.name, opt->max);
+			       opt->attr.name, opt_max);
 		return -BCH_ERR_ERANGE_option_too_big;
 	}
 
-- 
2.47.0