[PATCH 6.1.y] usb: gadget: f_mass_storage: fix null pointer dereference in fsg_common_set_num_buffers()

[Sasha Levin <sashal@kernel.org>]

From: Jeffin Philip <jeffinphilip14@gmail.com>

[ Upstream commit 2c0f5ca48674a5b5f9fa4a9c3325aa48053af0bc ]

Previously fsg_num_buffers_validate() was removed as it was not
necessary due to Kconfig setting the limits for n from 2 to 256 with
default as 2. However, setting the page content in such a way that
kstrtou8() reflects n value as either 0 or 1 bypasses these
restrictions leading to a null pointer dereference if n is 0. Fix
this by adding a check for n < 2 and returning -EINVAL if n is
either 0 or 1 consistent with Kconfig logic.

Reported-by: syzbot+791be35f1fbcc85d06d7@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=791be35f1fbcc85d06d7
Fixes: fe5a6c48fd95 ("usb: gadget: storage: get rid of fsg_num_buffers_validate()")
Cc: stable <stable@kernel.org>
Signed-off-by: Jeffin Philip <jeffinphilip14@gmail.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://patch.msgid.link/20260818035904.10324-1-jeffinphilip14@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ adjusted context to retain the branch’s existing kcalloc() call instead of kzalloc_objs(). ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/usb/gadget/function/f_mass_storage.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c
index e364b7b4d82b9..ea40f68a6e323 100644
--- a/drivers/usb/gadget/function/f_mass_storage.c
+++ b/drivers/usb/gadget/function/f_mass_storage.c
@@ -2747,6 +2747,9 @@ int fsg_common_set_num_buffers(struct fsg_common *common, unsigned int n)
 	struct fsg_buffhd *bh, *buffhds;
 	int i;
 
+	if (n < 2)
+		return -EINVAL;
+
 	buffhds = kcalloc(n, sizeof(*buffhds), GFP_KERNEL);
 	if (!buffhds)
 		return -ENOMEM;
-- 
2.53.0