From 58984ce21d315b70df1a43644df7416ea7c9bfd8 Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Thu, 2 Apr 2009 16:56:42 -0700 Subject: [PATCH] mm: do_xip_mapping_read: fix length calculation The calculation of the value nr in do_xip_mapping_read is incorrect. If the copy required more than one iteration in the do while loop the copies variable will be non-zero. The maximum length that may be passed to the call to copy_to_user(buf+copied, xip_mem+offset, nr) is len-copied but the check only compares against (nr > len). This bug is the cause for the heap corruption Carsten has been chasing for so long: *** glibc detected *** /bin/bash: free(): invalid next size (normal): 0x00000000800e39f0 *** ======= Backtrace: ========= /lib64/libc.so.6[0x200000b9b44] /lib64/libc.so.6(cfree+0x8e)[0x200000bdade] /bin/bash(free_buffered_stream+0x32)[0x80050e4e] /bin/bash(close_buffered_stream+0x1c)[0x80050ea4] /bin/bash(unset_bash_input+0x2a)[0x8001c366] /bin/bash(make_child+0x1d4)[0x8004115c] /bin/bash[0x8002fc3c] /bin/bash(execute_command_internal+0x656)[0x8003048e] /bin/bash(execute_command+0x5e)[0x80031e1e] /bin/bash(execute_command_internal+0x79a)[0x800305d2] /bin/bash(execute_command+0x5e)[0x80031e1e] /bin/bash(reader_loop+0x270)[0x8001efe0] /bin/bash(main+0x1328)[0x8001e960] /lib64/libc.so.6(__libc_start_main+0x100)[0x200000592a8] /bin/bash(clearerr+0x5e)[0x8001c092] With this bug fix the commit 0e4a9b59282914fe057ab17027f55123964bc2e2 "ext2/xip: refuse to change xip flag during remount with busy inodes" can be removed again. Cc: Carsten Otte Cc: Nick Piggin Cc: Jared Hulbert Cc: Signed-off-by: Martin Schwidefsky Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap_xip.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c index 0c04615651b7..427dfe3ce78c 100644 --- a/mm/filemap_xip.c +++ b/mm/filemap_xip.c @@ -89,8 +89,8 @@ do_xip_mapping_read(struct address_space *mapping, } } nr = nr - offset; - if (nr > len) - nr = len; + if (nr > len - copied) + nr = len - copied; error = mapping->a_ops->get_xip_mem(mapping, index, 0, &xip_mem, &xip_pfn); -- GitLab