From a01c7800420d2c294ca403988488a635d4087a6d Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Fri, 11 Dec 2009 15:48:23 -0800 Subject: [PATCH] nvram: Fix write beyond end condition; prove to gcc copy is safe In nvram_write, first of all, correctly handle the case where the file pointer is already beyond the end; we should return EOF in that case. Second, make the logic a bit more explicit so that gcc can statically prove that the copy_from_user() is safe. Once the condition of the beyond-end filepointer is eliminated, the copy is safe but gcc can't prove it, causing build failures for i386 allyesconfig. Third, eliminate the entirely superfluous variable "len", and just use the passed-in variable "count" instead. Signed-off-by: H. Peter Anvin Cc: Arjan van de Ven Cc: Andrew Morton Cc: Wim Van Sebroeck Cc: Frederic Weisbecker LKML-Reference: --- drivers/char/nvram.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/drivers/char/nvram.c b/drivers/char/nvram.c index 4008e2ce73c1..fdbcc9fd6d31 100644 --- a/drivers/char/nvram.c +++ b/drivers/char/nvram.c @@ -264,10 +264,16 @@ static ssize_t nvram_write(struct file *file, const char __user *buf, unsigned char contents[NVRAM_BYTES]; unsigned i = *ppos; unsigned char *tmp; - int len; - len = (NVRAM_BYTES - i) < count ? (NVRAM_BYTES - i) : count; - if (copy_from_user(contents, buf, len)) + if (i >= NVRAM_BYTES) + return 0; /* Past EOF */ + + if (count > NVRAM_BYTES - i) + count = NVRAM_BYTES - i; + if (count > NVRAM_BYTES) + return -EFAULT; /* Can't happen, but prove it to gcc */ + + if (copy_from_user(contents, buf, count)) return -EFAULT; spin_lock_irq(&rtc_lock); @@ -275,7 +281,7 @@ static ssize_t nvram_write(struct file *file, const char __user *buf, if (!__nvram_check_checksum()) goto checksum_err; - for (tmp = contents; count-- > 0 && i < NVRAM_BYTES; ++i, ++tmp) + for (tmp = contents; count--; ++i, ++tmp) __nvram_write_byte(*tmp, i); __nvram_set_checksum(); -- 2.20.1