take security_mmap_file() outside of ->mmap_sem

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/security.h

@@ -1745,8 +1745,8 @@ int security_file_permission(struct file *file, int mask);
 int security_file_alloc(struct file *file);
 void security_file_free(struct file *file);
 int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
-int security_mmap_file(struct file *file, unsigned long reqprot,
-			unsigned long prot, unsigned long flags);
+int security_mmap_file(struct file *file, unsigned long prot,
+			unsigned long flags);
 int security_mmap_addr(unsigned long addr);
 int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
 			   unsigned long prot);
@@ -2183,8 +2183,7 @@ static inline int security_file_ioctl(struct file *file, unsigned int cmd,
 	return 0;
 }
 
-static inline int security_mmap_file(struct file *file, unsigned long reqprot,
-				     unsigned long prot,
+static inline int security_mmap_file(struct file *file, unsigned long prot,
 				     unsigned long flags)
 {
 	return 0;

ipc/shm.c

@@ -1036,6 +1036,10 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
 	sfd->file = shp->shm_file;
 	sfd->vm_ops = NULL;
 
+	err = security_mmap_file(file, prot, flags);
+	if (err)
+		goto out_fput;
+
 	down_write(&current->mm->mmap_sem);
 	if (addr && !(shmflg & SHM_REMAP)) {
 		err = -EINVAL;
@@ -1058,6 +1062,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
 invalid:
 	up_write(&current->mm->mmap_sem);
 
+out_fput:
 	fput(file);
 
 out_nattch:

mm/mmap.c

@@ -979,7 +979,6 @@ static unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
 	struct inode *inode;
 	vm_flags_t vm_flags;
 	int error;
-	unsigned long reqprot = prot;
 
 	/*
 	 * Does the application expect PROT_READ to imply PROT_EXEC?
@@ -1105,10 +1104,6 @@ static unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
 	if (error)
 		return error;
 
-	error = security_mmap_file(file, reqprot, prot, flags);
-	if (error)
-		return error;
-
 	return mmap_region(file, addr, len, flags, vm_flags, pgoff);
 }
 
@@ -1130,9 +1125,12 @@ unsigned long vm_mmap(struct file *file, unsigned long addr,
 	unsigned long ret;
 	struct mm_struct *mm = current->mm;
 
-	down_write(&mm->mmap_sem);
-	ret = do_mmap(file, addr, len, prot, flag, offset);
-	up_write(&mm->mmap_sem);
+	ret = security_mmap_file(file, prot, flag);
+	if (!ret) {
+		down_write(&mm->mmap_sem);
+		ret = do_mmap(file, addr, len, prot, flag, offset);
+		up_write(&mm->mmap_sem);
+	}
 	return ret;
 }
 EXPORT_SYMBOL(vm_mmap);
@@ -1168,9 +1166,12 @@ SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
 
 	flags &= ~(MAP_EXECUTABLE | MAP_DENYWRITE);
 
-	down_write(&current->mm->mmap_sem);
-	retval = do_mmap_pgoff(file, addr, len, prot, flags, pgoff);
-	up_write(&current->mm->mmap_sem);
+	retval = security_mmap_file(file, prot, flags);
+	if (!retval) {
+		down_write(&current->mm->mmap_sem);
+		retval = do_mmap_pgoff(file, addr, len, prot, flags, pgoff);
+		up_write(&current->mm->mmap_sem);
+	}
 
 	if (file)
 		fput(file);

mm/nommu.c

@@ -889,7 +889,6 @@ static int validate_mmap_request(struct file *file,
 				 unsigned long *_capabilities)
 {
 	unsigned long capabilities, rlen;
-	unsigned long reqprot = prot;
 	int ret;
 
 	/* do the simple checks first */
@@ -1048,9 +1047,6 @@ static int validate_mmap_request(struct file *file,
 
 	/* allow the security API to have its say */
 	ret = security_mmap_addr(addr);
-	if (ret < 0)
-		return ret;
-	ret = security_mmap_file(file, reqprot, prot, flags);
 	if (ret < 0)
 		return ret;
 
@@ -1492,9 +1488,12 @@ unsigned long vm_mmap(struct file *file, unsigned long addr,
 	unsigned long ret;
 	struct mm_struct *mm = current->mm;
 
-	down_write(&mm->mmap_sem);
-	ret = do_mmap(file, addr, len, prot, flag, offset);
-	up_write(&mm->mmap_sem);
+	ret = security_mmap_file(file, prot, flag);
+	if (!ret) {
+		down_write(&mm->mmap_sem);
+		ret = do_mmap(file, addr, len, prot, flag, offset);
+		up_write(&mm->mmap_sem);
+	}
 	return ret;
 }
 EXPORT_SYMBOL(vm_mmap);
@@ -1515,9 +1514,12 @@ SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
 
 	flags &= ~(MAP_EXECUTABLE | MAP_DENYWRITE);
 
-	down_write(&current->mm->mmap_sem);
-	retval = do_mmap_pgoff(file, addr, len, prot, flags, pgoff);
-	up_write(&current->mm->mmap_sem);
+	ret = security_mmap_file(file, prot, flags);
+	if (!ret) {
+		down_write(&current->mm->mmap_sem);
+		retval = do_mmap_pgoff(file, addr, len, prot, flags, pgoff);
+		up_write(&current->mm->mmap_sem);
+	}
 
 	if (file)
 		fput(file);

security/security.c

@@ -20,6 +20,9 @@
 #include <linux/ima.h>
 #include <linux/evm.h>
 #include <linux/fsnotify.h>
+#include <linux/mman.h>
+#include <linux/mount.h>
+#include <linux/personality.h>
 #include <net/flow.h>
 
 #define MAX_LSM_EVM_XATTR	2
@@ -657,11 +660,35 @@ int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	return security_ops->file_ioctl(file, cmd, arg);
 }
 
-int security_mmap_file(struct file *file, unsigned long reqprot,
-			unsigned long prot, unsigned long flags)
+int security_mmap_file(struct file *file, unsigned long prot,
+			unsigned long flags)
 {
+	unsigned long reqprot = prot;
 	int ret;
-
+	/*
+	 * Does the application expect PROT_READ to imply PROT_EXEC?
+	 *
+	 * (the exception is when the underlying filesystem is noexec
+	 *  mounted, in which case we dont add PROT_EXEC.)
+	 */
+	if (!(reqprot & PROT_READ))
+		goto out;
+	if (!(current->personality & READ_IMPLIES_EXEC))
+		goto out;
+	if (!file) {
+		prot |= PROT_EXEC;
+	} else if (!(file->f_path.mnt->mnt_flags & MNT_NOEXEC)) {
+#ifndef CONFIG_MMU
+		unsigned long caps = 0;
+		struct address_space *mapping = file->f_mapping;
+		if (mapping && mapping->backing_dev_info)
+			caps = mapping->backing_dev_info->capabilities;
+		if (!(caps & BDI_CAP_EXEC_MAP))
+			goto out;
+#endif
+		prot |= PROT_EXEC;
+	}
+out:
 	ret = security_ops->mmap_file(file, reqprot, prot, flags);
 	if (ret)
 		return ret;