[PATCH v2 16/51] PNP: isapnp: don't read past the end of the buffer on a large pread()

[Christian Brauner]

isapnp_proc_bus_read() truncates the position to an int. A pread() at
an offset like 0xfffffc00 turns it negative, the check against the size
of the configuration space passes, and the loop then puts everything
from that position up to byte 256 into the reader's buffer, no matter
how few bytes were asked for.

Keep the position as a loff_t and clamp the count against what is left
of the configuration space.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Rafael J. Wysocki (Intel) <rafael at kernel.org>
Cc: stable at vger.kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner at kernel.org>
---
 drivers/pnp/isapnp/proc.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/pnp/isapnp/proc.c b/drivers/pnp/isapnp/proc.c
index b3abab24050b..1829c20d5446 100644
--- a/drivers/pnp/isapnp/proc.c
+++ b/drivers/pnp/isapnp/proc.c
@@ -23,15 +23,13 @@ static ssize_t isapnp_proc_bus_read(struct file *file, char __user * buf,
 				    size_t nbytes, loff_t * ppos)
 {
 	struct pnp_dev *dev = pde_data(file_inode(file));
-	int pos = *ppos;
+	loff_t pos = *ppos;
 	int cnt, size = 256;
 	int ret;
 
 	if (pos >= size)
 		return 0;
-	if (nbytes >= size)
-		nbytes = size;
-	if (pos + nbytes > size)
+	if (nbytes > size - pos)
 		nbytes = size - pos;
 	cnt = nbytes;
 

-- 
2.53.0