Back in 2.1.29 the clear_user() guts (__bzero()) had been merged
with memset(). Unfortunately, while all exception handlers had been
copied, one of the exception table entries got lost. As the result,
clear_user() starting at 128*n bytes before the end of page and
spanning between 8 and 127 bytes into the next page would oops when
the second page is unmapped. It's trivial to reproduce - all
it takes is
main()
{
int fd = open("/dev/zero", O_RDONLY);
char *p = mmap(NULL, 16384, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANON, -1, 0);
munmap(p + 8192, 8192);
read(fd, p + 8192 - 128, 192);
}
which had been oopsing since March 1997. Says something about
the quality of test coverage... ;-/ And while today sparc32 port
is nearly dead, back in '97 it had been very much alive; in fact,
sparc64 had only been in mainline for 3 months by that point...
Cc: stable@xxxxxxxxxx
Fixes: v2.1.29
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
diff --git a/arch/sparc/lib/memset.S b/arch/sparc/lib/memset.S
index b89d42b29e34..f427f34b8b79 100644
--- a/arch/sparc/lib/memset.S
+++ b/arch/sparc/lib/memset.S
@@ -142,6 +142,7 @@ __bzero:
ZERO_LAST_BLOCKS(%o0, 0x48, %g2)
ZERO_LAST_BLOCKS(%o0, 0x08, %g2)
13:
+ EXT(12b, 13b, 21f)
be 8f
andcc %o1, 4, %g0
