Hi,
The mmap() call fails when addr is specified, MAP_FIXED is cleared in
flags and no address space can be allocated either at addr or above it.
This is a legal request and it should not fail as long as there is space
available below addr. Following is a patch that fixes the problem.
This is nothing new -- I already submitted a similar patch against
2.4.0-test4 once upon a time. This patch is clean(er), though, and I
believe it can be safely applied to the upcoming 2.4.5 release.
A simple test case to trigger the current mmap() bad behaviour for 32-bit
CPUs is something like:
fd = open("/dev/zero", O_RDONLY);
p = mmap((void *)0xfffff000, 4096, PROT_READ, MAP_SHARED, fd, 0);
With my patch the code does not fail anymore -- p is set to an available
address lower than 0xfffff000.
The bug was discovered when tracking down the reason of dlopen() failures
when called from statically linked binaries on MIPS/Linux. The patch
fixes them.
Maciej
--
+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+--------------------------------------------------------------+
+ e-mail: [EMAIL PROTECTED], PGP key available +
diff -up --recursive --new-file linux-2.4.4.macro/mm/mmap.c linux-2.4.4/mm/mmap.c
--- linux-2.4.4.macro/mm/mmap.c Tue May 1 17:24:25 2001
+++ linux-2.4.4/mm/mmap.c Tue May 1 18:23:25 2001
@@ -219,7 +219,7 @@ unsigned long do_mmap_pgoff(struct file
if ((len = PAGE_ALIGN(len)) == 0)
return addr;
- if (len > TASK_SIZE || addr > TASK_SIZE-len)
+ if (len > TASK_SIZE)
return -EINVAL;
/* offset overflow? */
@@ -405,9 +405,15 @@ static inline unsigned long arch_get_unm
if (len > TASK_SIZE)
return -ENOMEM;
- if (!addr)
- addr = TASK_UNMAPPED_BASE;
- addr = PAGE_ALIGN(addr);
+
+ if (addr) {
+ addr = PAGE_ALIGN(addr);
+ vma = find_vma(current->mm, addr);
+ if (TASK_SIZE - len >= addr &&
+ (!vma || addr + len <= vma->vm_start))
+ return addr;
+ }
+ addr = PAGE_ALIGN(TASK_UNMAPPED_BASE);
for (vma = find_vma(current->mm, addr); ; vma = vma->vm_next) {
/* At this point: (!vma || addr < vma->vm_end). */
@@ -425,6 +431,8 @@ extern unsigned long arch_get_unmapped_a
unsigned long get_unmapped_area(struct file *file, unsigned long addr, unsigned long
len, unsigned long pgoff, unsigned long flags)
{
if (flags & MAP_FIXED) {
+ if (addr > TASK_SIZE - len)
+ return -EINVAL;
if (addr & ~PAGE_MASK)
return -EINVAL;
return addr;
-
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