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do_brk() needs mmap_sem write-locked

PATCH In review Marcelo Tosatti 3 participants 4 messages Jan 12, 2005 – Jan 13, 2005

Subsystems (5)
Memory management VFS MIPS exec and binfmt +1 more subsystems
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Marcelo Tosatti

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#0 lore raw

PATCH 1/1 do_brk() needs mmap_sem write-locked

Hi Linus,

It seems to be general consensus that its safer to require all do_brk() callers to grab mmap_sem, and have do_brk to warn otherwise. This is what the following patch does.

Similar version has been changed to in v2.4.

Please apply

arch/mips/kernel/irixelf.c +10 -1
diff -Nur linux-2.6-curr.orig/arch/mips/kernel/irixelf.c linux-2.6-curr/arch/mips/kernel/irixelf.c
@@ -127,7 +127,9 @@
 	end = PAGE_ALIGN(end);
 	if (end <= start)
 		return;
+	down_write(&current->mm->mmap_sem);
 	do_brk(start, end - start);
+	up_write(&current->mm->mmap_sem);
 }
 
 

@@ -375,7 +377,9 @@
 
 	/* Map the last of the bss segment */
 	if (last_bss > len) {
+		down_write(&current->mm->mmap_sem);
 		do_brk(len, (last_bss - len));
+		up_write(&current->mm->mmap_sem);
 	}
 	kfree(elf_phdata);
 

@@ -562,7 +566,9 @@
 	unsigned long v;
 	struct prda *pp;
 
+	down_write(&current->mm->mmap_sem);
 	v =  do_brk (PRDA_ADDRESS, PAGE_SIZE);
+	up_write(&current->mm->mmap_sem);
 
 	if (v < 0)
 		return;

@@ -852,8 +858,11 @@
 
 	len = (elf_phdata->p_filesz + elf_phdata->p_vaddr+ 0xfff) & 0xfffff000;
 	bss = elf_phdata->p_memsz + elf_phdata->p_vaddr;
-	if (bss > len)
+	if (bss > len) {
+	  down_write(&current->mm->mmap_sem);
 	  do_brk(len, bss-len);
+	  up_write(&current->mm->mmap_sem);
+	}
 	kfree(elf_phdata);
 	return 0;
 }
arch/sparc64/kernel/binfmt_aout32.c +12 -0
diff -Nur linux-2.6-curr.orig/arch/sparc64/kernel/binfmt_aout32.c linux-2.6-curr/arch/sparc64/kernel/binfmt_aout32.c
@@ -49,7 +49,9 @@
 	end = PAGE_ALIGN(end);
 	if (end <= start)
 		return;
+	down_write(&current->mm->mmap_sem);
 	do_brk(start, end - start);
+	up_write(&current->mm->mmap_sem);
 }
 
 /*

@@ -246,10 +248,14 @@
 	if (N_MAGIC(ex) == NMAGIC) {
 		loff_t pos = fd_offset;
 		/* Fuck me plenty... */
+		down_write(&current->mm->mmap_sem);	
 		error = do_brk(N_TXTADDR(ex), ex.a_text);
+		up_write(&current->mm->mmap_sem);
 		bprm->file->f_op->read(bprm->file, (char __user *)N_TXTADDR(ex),
 			  ex.a_text, &pos);
+		down_write(&current->mm->mmap_sem);
 		error = do_brk(N_DATADDR(ex), ex.a_data);
+		up_write(&current->mm->mmap_sem);
 		bprm->file->f_op->read(bprm->file, (char __user *)N_DATADDR(ex),
 			  ex.a_data, &pos);
 		goto beyond_if;

@@ -257,8 +263,10 @@
 
 	if (N_MAGIC(ex) == OMAGIC) {
 		loff_t pos = fd_offset;
+		down_write(&current->mm->mmap_sem);
 		do_brk(N_TXTADDR(ex) & PAGE_MASK,
 			ex.a_text+ex.a_data + PAGE_SIZE - 1);
+		up_write(&current->mm->mmap_sem);
 		bprm->file->f_op->read(bprm->file, (char __user *)N_TXTADDR(ex),
 			  ex.a_text+ex.a_data, &pos);
 	} else {

@@ -272,7 +280,9 @@
 
 		if (!bprm->file->f_op->mmap) {
 			loff_t pos = fd_offset;
+			down_write(&current->mm->mmap_sem);
 			do_brk(0, ex.a_text+ex.a_data);
+			up_write(&current->mm->mmap_sem);
 			bprm->file->f_op->read(bprm->file,
 				  (char __user *)N_TXTADDR(ex),
 				  ex.a_text+ex.a_data, &pos);

@@ -389,7 +399,9 @@
 	len = PAGE_ALIGN(ex.a_text + ex.a_data);
 	bss = ex.a_text + ex.a_data + ex.a_bss;
 	if (bss > len) {
+		down_write(&current->mm->mmap_sem);
 		error = do_brk(start_addr + len, bss - len);
+		up_write(&current->mm->mmap_sem);
 		retval = error;
 		if (error != start_addr + len)
 			goto out;
arch/x86_64/ia32/ia32_aout.c +11 -1
diff -Nur linux-2.6-curr.orig/arch/x86_64/ia32/ia32_aout.c linux-2.6-curr/arch/x86_64/ia32/ia32_aout.c
@@ -115,7 +115,9 @@
 	end = PAGE_ALIGN(end);
 	if (end <= start)
 		return;
+	down_write(&current->mm->mmap_sem);
 	do_brk(start, end - start);
+	up_write(&current->mm->mmap_sem);
 }
 
 #if CORE_DUMP

@@ -325,7 +327,10 @@
 		pos = 32;
 		map_size = ex.a_text+ex.a_data;
 
+		down_write(&current->mm->mmap_sem);
 		error = do_brk(text_addr & PAGE_MASK, map_size);
+		up_write(&current->mm->mmap_sem);
+
 		if (error != (text_addr & PAGE_MASK)) {
 			send_sig(SIGKILL, current, 0);
 			return error;

@@ -361,7 +366,9 @@
 
 		if (!bprm->file->f_op->mmap||((fd_offset & ~PAGE_MASK) != 0)) {
 			loff_t pos = fd_offset;
+			down_write(&current->mm->mmap_sem);
 			do_brk(N_TXTADDR(ex), ex.a_text+ex.a_data);
+			up_write(&current->mm->mmap_sem);
 			bprm->file->f_op->read(bprm->file,(char *)N_TXTADDR(ex),
 					ex.a_text+ex.a_data, &pos);
 			flush_icache_range((unsigned long) N_TXTADDR(ex),

@@ -469,8 +476,9 @@
 			error_time = jiffies;
 		}
 #endif
-
+		down_write(&current->mm->mmap_sem);
 		do_brk(start_addr, ex.a_text + ex.a_data + ex.a_bss);
+		up_write(&current->mm->mmap_sem);
 		
 		file->f_op->read(file, (char *)start_addr,
 			ex.a_text + ex.a_data, &pos);

@@ -494,7 +502,9 @@
 	len = PAGE_ALIGN(ex.a_text + ex.a_data);
 	bss = ex.a_text + ex.a_data + ex.a_bss;
 	if (bss > len) {
+		down_write(&current->mm->mmap_sem);
 		error = do_brk(start_addr + len, bss - len);
+		up_write(&current->mm->mmap_sem);
 		retval = error;
 		if (error != start_addr + len)
 			goto out;
fs/binfmt_aout.c +14 -3
diff -Nur linux-2.6-curr.orig/fs/binfmt_aout.c linux-2.6-curr/fs/binfmt_aout.c
@@ -50,7 +50,10 @@
 	start = PAGE_ALIGN(start);
 	end = PAGE_ALIGN(end);
 	if (end > start) {
-		unsigned long addr = do_brk(start, end - start);
+		unsigned long addr;
+		down_write(&current->mm->mmap_sem);
+		addr = do_brk(start, end - start);
+		up_write(&current->mm->mmap_sem);
 		if (BAD_ADDR(addr))
 			return addr;
 	}

@@ -323,10 +326,14 @@
 		loff_t pos = fd_offset;
 		/* Fuck me plenty... */
 		/* <AOL></AOL> */
+		down_write(&current->mm->mmap_sem);	
 		error = do_brk(N_TXTADDR(ex), ex.a_text);
+		up_write(&current->mm->mmap_sem);
 		bprm->file->f_op->read(bprm->file, (char *) N_TXTADDR(ex),
 			  ex.a_text, &pos);
+		down_write(&current->mm->mmap_sem);
 		error = do_brk(N_DATADDR(ex), ex.a_data);
+		up_write(&current->mm->mmap_sem);
 		bprm->file->f_op->read(bprm->file, (char *) N_DATADDR(ex),
 			  ex.a_data, &pos);
 		goto beyond_if;

@@ -346,8 +353,9 @@
 		pos = 32;
 		map_size = ex.a_text+ex.a_data;
 #endif
-
+		down_write(&current->mm->mmap_sem);
 		error = do_brk(text_addr & PAGE_MASK, map_size);
+		up_write(&current->mm->mmap_sem);
 		if (error != (text_addr & PAGE_MASK)) {
 			send_sig(SIGKILL, current, 0);
 			return error;

@@ -382,7 +390,9 @@
 
 		if (!bprm->file->f_op->mmap||((fd_offset & ~PAGE_MASK) != 0)) {
 			loff_t pos = fd_offset;
+			down_write(&current->mm->mmap_sem);
 			do_brk(N_TXTADDR(ex), ex.a_text+ex.a_data);
+			up_write(&current->mm->mmap_sem);
 			bprm->file->f_op->read(bprm->file,
 					(char __user *)N_TXTADDR(ex),
 					ex.a_text+ex.a_data, &pos);

@@ -487,8 +497,9 @@
 			       file->f_dentry->d_name.name);
 			error_time = jiffies;
 		}
-
+		down_write(&current->mm->mmap_sem);
 		do_brk(start_addr, ex.a_text + ex.a_data + ex.a_bss);
+		up_write(&current->mm->mmap_sem);
 		
 		file->f_op->read(file, (char __user *)start_addr,
 			ex.a_text + ex.a_data, &pos);
fs/binfmt_elf.c +11 -1
@@ -88,7 +88,10 @@
 	start = ELF_PAGEALIGN(start);
 	end = ELF_PAGEALIGN(end);
 	if (end > start) {
-		unsigned long addr = do_brk(start, end - start);
+		unsigned long addr;
+		down_write(&current->mm->mmap_sem);
+		addr = do_brk(start, end - start);
+		up_write(&current->mm->mmap_sem);
 		if (BAD_ADDR(addr))
 			return addr;
 	}

@@ -408,7 +411,9 @@
 
 	/* Map the last of the bss segment */
 	if (last_bss > elf_bss) {
+		down_write(&current->mm->mmap_sem);
 		error = do_brk(elf_bss, last_bss - elf_bss);
+		up_write(&current->mm->mmap_sem);
 		if (BAD_ADDR(error))
 			goto out_close;
 	}

@@ -448,7 +453,9 @@
 		goto out;
 	}
 
+	down_write(&current->mm->mmap_sem);	
 	do_brk(0, text_data);
+	up_write(&current->mm->mmap_sem);
 	if (!interpreter->f_op || !interpreter->f_op->read)
 		goto out;
 	if (interpreter->f_op->read(interpreter, addr, text_data, &offset) < 0)

@@ -456,8 +463,11 @@
 	flush_icache_range((unsigned long)addr,
 	                   (unsigned long)addr + text_data);
 
+
+	down_write(&current->mm->mmap_sem);	
 	do_brk(ELF_PAGESTART(text_data + ELF_MIN_ALIGN - 1),
 		interp_ex->a_bss);
+	up_write(&current->mm->mmap_sem);
 	elf_entry = interp_ex->a_entry;
 
 out:
mm/mmap.c +6 -0
diff -Nur linux-2.6-curr.orig/mm/mmap.c linux-2.6-curr/mm/mmap.c
@@ -1891,6 +1891,12 @@
 	}
 
 	/*
+	 * mm->mmap_sem is required to protect against another thread
+	 * changing the mappings in case we sleep.
+	 */
+	WARN_ON(down_read_trylock(&mm->mmap_sem));
+
+	/*
 	 * Clear old maps.  this also does some error checking for us
 	 */
  munmap_back:
#1 lore raw

Looks good, except for a small nit:

Quoted 7 lines · Marcelo Tosatti

diff -Nur linux-2.6-curr.orig/mm/mmap.c linux-2.6-curr/mm/mmap.c

mm/mmap.c +0 -0
@@ -1891,6 +1891,12 @@
 	}

mm/mmap.c line 1902

Quoted 10 lines
mm/mmap.c +6 -0
 	/*
+	 * mm->mmap_sem is required to protect against another thread
+	 * changing the mappings in case we sleep.
+	 */
+	WARN_ON(down_read_trylock(&mm->mmap_sem));
+
+	/*
 	 * Clear old maps.  this also does some error checking for us
 	 */
  munmap_back:

if that warning ever triggers, mmap_sem will now be locked, and that will cause problems. So I suspect it's better to do

	if (down_read_trylock(&mm->mmap_sem)) {
		WARN_ON(1);
		up_read(&mm->mmap_sem);
	}

and move that into a helper function of its own (something like "verify_mmap_write_lock_held()").

Linus

author
#2 lore raw
Quoted 26 lines · Linus Torvalds

Looks good, except for a small nit:

Quoted 7 lines · Marcelo Tosatti

diff -Nur linux-2.6-curr.orig/mm/mmap.c linux-2.6-curr/mm/mmap.c

mm/mmap.c +0 -0
@@ -1891,6 +1891,12 @@
 	}

mm/mmap.c line 1902

Quoted 10 lines
mm/mmap.c +6 -0
 	/*
+	 * mm->mmap_sem is required to protect against another thread
+	 * changing the mappings in case we sleep.
+	 */
+	WARN_ON(down_read_trylock(&mm->mmap_sem));
+
+	/*
 	 * Clear old maps.  this also does some error checking for us
 	 */
  munmap_back:

if that warning ever triggers, mmap_sem will now be locked, and that will cause problems. So I suspect it's better to do

Quoted 7 lines
	if (down_read_trylock(&mm->mmap_sem)) {
		WARN_ON(1);
		up_read(&mm->mmap_sem);
	}

and move that into a helper function of its own (something like "verify_mmap_write_lock_held()").

OK - I've seen you just committed a fix.

I've fixed v2.4 version.

#3 lore raw
In reply to Linus Torvalds
Quoted 6 lines · Linus Torvalds

if that warning ever triggers, mmap_sem will now be locked, and that will cause problems. So I suspect it's better to do

	if (down_read_trylock(&mm->mmap_sem)) {
		WARN_ON(1);
		up_read(&mm->mmap_sem);

Better to leave the lock held and remember the error then drop it at the end - anything else means the WARN_ON case is a security hole.