4.9-stable review patch. If anyone has any objections, please let me know.
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From: Jann Horn jannh@google.com
[ Upstream commit 6c6bc9ea84d0008024606bf5ba10519e20d851bf ]
The first checks in mtdchar_read() and mtdchar_write() attempt to limit `count` such that `*ppos + count <= mtd->size`. However, they ignore the possibility of `*ppos > mtd->size`, allowing the calculation of `count` to wrap around. `mtdchar_lseek()` prevents seeking beyond mtd->size, but the pread/pwrite syscalls bypass this.
I haven't found any codepath on which this actually causes dangerous behavior, but it seems like a sensible change anyway.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Jann Horn jannh@google.com Signed-off-by: Boris Brezillon boris.brezillon@bootlin.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/mtd/mtdchar.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
--- a/drivers/mtd/mtdchar.c +++ b/drivers/mtd/mtdchar.c @@ -160,8 +160,12 @@ static ssize_t mtdchar_read(struct file
pr_debug("MTD_read\n");
- if (*ppos + count > mtd->size) - count = mtd->size - *ppos; + if (*ppos + count > mtd->size) { + if (*ppos < mtd->size) + count = mtd->size - *ppos; + else + count = 0; + }
if (!count) return 0; @@ -246,7 +250,7 @@ static ssize_t mtdchar_write(struct file
pr_debug("MTD_write\n");
- if (*ppos == mtd->size) + if (*ppos >= mtd->size) return -ENOSPC;
if (*ppos + count > mtd->size)