[PATCH] do_brk() needs mmap_sem write-locked

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.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 25 insertions, 4 deletions

diff --git a/fs/binfmt_aout.c b/fs/binfmt_aout.c
index 8075fdff23646c..a53d9a9e0de4ae 100644
--- a/fs/binfmt_aout.c
+++ b/fs/binfmt_aout.c
@@ -50,7 +50,10 @@ static int set_brk(unsigned long start, unsigned long end)
 	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 @@ static int load_aout_binary(struct linux_binprm * bprm, struct pt_regs * regs)
 		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 @@ static int load_aout_binary(struct linux_binprm * bprm, struct pt_regs * regs)
 		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 @@ static int load_aout_binary(struct linux_binprm * bprm, struct pt_regs * regs)
 
 		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 @@ static int load_aout_library(struct file *file)
 			       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);
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index a66bc8df6d6f9b..6eb6971bdee2b1 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -88,7 +88,10 @@ static int set_brk(unsigned long start, unsigned long end)
 	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;
 	}
@@ -409,7 +412,9 @@ static unsigned long load_elf_interp(struct elfhdr * interp_elf_ex,
 
 	/* 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;
 	}
@@ -449,7 +454,9 @@ static unsigned long load_aout_interp(struct exec * interp_ex,
 		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)
@@ -457,8 +464,11 @@ static unsigned long load_aout_interp(struct exec * interp_ex,
 	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: