[PATCH] generic arch_get_unmapped_area(): make sure that addr >= TASK_UNMAPPED_BASE

From: Krzysztof Mazur
Date: Mon Jun 22 2009 - 09:37:58 EST


Generic arch_get_unmapped_area() use mm->free_area_cache for start_addr
and addr even when it's smaller that TASK_UNMAPPED_BASE.

if (len > mm->cached_hole_size) {
start_addr = addr = mm->free_area_cache;
} else {
start_addr = addr = TASK_UNMAPPED_BASE;
mm->cached_hole_size = 0;
}

I don't know how it should work (maybe mm->free_area_cache should be
never smaller than TASK_UNMAPPED_BASE, but it was 0 when I took strace
below), but I copied code from x86-64's arch_get_unmapped_area(),
there is:

if (((flags & MAP_32BIT) || test_thread_flag(TIF_IA32))
&& len <= mm->cached_hole_size) {
mm->cached_hole_size = 0;
mm->free_area_cache = begin;
}
addr = mm->free_area_cache;
if (addr < begin)
addr = begin;
start_addr = addr;

Now with check for begin (TASK_UNMAPPED_BASE in generic code) it seems
to be ok.

Previously I had -EACCESS when process used legacy VA layout (for instance
because of no RLIMIT_STACK limit):

setrlimit(RLIMIT_STACK, {rlim_cur=RLIM_INFINITY, rlim_max=RLIM_INFINITY}) = 0
...
vfork(Process 1819 attached (waiting for parent)
Process 1819 resumed (parent 1818 ready)
) = 1819
[pid 1819] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid 1819] execve("/bin/sh", ["/bin/sh", "-c", "if test ! -f config.h; then \\\n "...], [/* 26 vars */]) = 0
[pid 1819] brk(0) = 0x8a01000
[pid 1819] uname({sys="Linux", node="geronimo", ...}) = 0
[pid 1819] access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
[pid 1819] open("/etc/ld.so.cache", O_RDONLY) = 3
[pid 1819] fstat64(3, {st_mode=S_IFREG|0644, st_size=105204, ...}) = 0
[pid 1819] mmap2(NULL, 105204, PROT_READ, MAP_PRIVATE, 3, 0) = -1 EACCES (Permission denied)

Signed-off-by: Krzysztof Mazur <krzysiek@xxxxxxxxxxxx>
---
mm/mmap.c | 13 ++++++++-----
1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 34579b2..577cfc0 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1289,12 +1289,15 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
(!vma || addr + len <= vma->vm_start))
return addr;
}
- if (len > mm->cached_hole_size) {
- start_addr = addr = mm->free_area_cache;
- } else {
- start_addr = addr = TASK_UNMAPPED_BASE;
- mm->cached_hole_size = 0;
+
+ if (len <= mm->cached_hole_size) {
+ mm->free_area_cache = TASK_UNMAPPED_BASE;
+ mm->cached_hole_size = 0;
}
+ addr = mm->free_area_cache;
+ if (addr < TASK_UNMAPPED_BASE)
+ addr = TASK_UNMAPPED_BASE;
+ start_addr = addr;

full_search:
for (vma = find_vma(mm, addr); ; vma = vma->vm_next) {
--
1.5.1.3

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/