fs/binfmt_elf.c: extract elf_read() function

ELF reads done by the kernel have very complicated error detection code
which better live in one place.

Link: http://lkml.kernel.org/r/20191005165215.GB26927@avx2Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/binfmt_elf.c

@@ -404,6 +404,17 @@ static unsigned long total_mapping_size(const struct elf_phdr *cmds, int nr)
 				ELF_PAGESTART(cmds[first_idx].p_vaddr);
 }
 
+static int elf_read(struct file *file, void *buf, size_t len, loff_t pos)
+{
+	ssize_t rv;
+
+	rv = kernel_read(file, buf, len, &pos);
+	if (unlikely(rv != len)) {
+		return (rv < 0) ? rv : -EIO;
+	}
+	return 0;
+}
+
 /**
  * load_elf_phdrs() - load ELF program headers
  * @elf_ex:   ELF header of the binary whose program headers should be loaded
@@ -418,7 +429,6 @@ static struct elf_phdr *load_elf_phdrs(const struct elfhdr *elf_ex,
 {
 	struct elf_phdr *elf_phdata = NULL;
 	int retval, err = -1;
-	loff_t pos = elf_ex->e_phoff;
 	unsigned int size;
 
 	/*
@@ -439,9 +449,9 @@ static struct elf_phdr *load_elf_phdrs(const struct elfhdr *elf_ex,
 		goto out;
 
 	/* Read in the program headers */
-	retval = kernel_read(elf_file, elf_phdata, size, &pos);
-	if (retval != size) {
-		err = (retval < 0) ? retval : -EIO;
+	retval = elf_read(elf_file, elf_phdata, size, elf_ex->e_phoff);
+	if (retval < 0) {
+		err = retval;
 		goto out;
 	}
 
@@ -720,7 +730,6 @@ static int load_elf_binary(struct linux_binprm *bprm)
 	elf_ppnt = elf_phdata;
 	for (i = 0; i < loc->elf_ex.e_phnum; i++, elf_ppnt++) {
 		char *elf_interpreter;
-		loff_t pos;
 
 		if (elf_ppnt->p_type != PT_INTERP)
 			continue;
@@ -738,14 +747,10 @@ static int load_elf_binary(struct linux_binprm *bprm)
 		if (!elf_interpreter)
 			goto out_free_ph;
 
-		pos = elf_ppnt->p_offset;
-		retval = kernel_read(bprm->file, elf_interpreter,
-				     elf_ppnt->p_filesz, &pos);
-		if (retval != elf_ppnt->p_filesz) {
-			if (retval >= 0)
-				retval = -EIO;
+		retval = elf_read(bprm->file, elf_interpreter, elf_ppnt->p_filesz,
+				  elf_ppnt->p_offset);
+		if (retval < 0)
 			goto out_free_interp;
-		}
 		/* make sure path is NULL terminated */
 		retval = -ENOEXEC;
 		if (elf_interpreter[elf_ppnt->p_filesz - 1] != '\0')
@@ -764,14 +769,10 @@ static int load_elf_binary(struct linux_binprm *bprm)
 		would_dump(bprm, interpreter);
 
 		/* Get the exec headers */
-		pos = 0;
-		retval = kernel_read(interpreter, &loc->interp_elf_ex,
-				     sizeof(loc->interp_elf_ex), &pos);
-		if (retval != sizeof(loc->interp_elf_ex)) {
-			if (retval >= 0)
-				retval = -EIO;
+		retval = elf_read(interpreter, &loc->interp_elf_ex,
+				  sizeof(loc->interp_elf_ex), 0);
+		if (retval < 0)
 			goto out_free_dentry;
-		}
 
 		break;
 
@@ -1174,11 +1175,10 @@ static int load_elf_library(struct file *file)
 	unsigned long elf_bss, bss, len;
 	int retval, error, i, j;
 	struct elfhdr elf_ex;
-	loff_t pos = 0;
 
 	error = -ENOEXEC;
-	retval = kernel_read(file, &elf_ex, sizeof(elf_ex), &pos);
-	if (retval != sizeof(elf_ex))
+	retval = elf_read(file, &elf_ex, sizeof(elf_ex), 0);
+	if (retval < 0)
 		goto out;
 
 	if (memcmp(elf_ex.e_ident, ELFMAG, SELFMAG) != 0)
@@ -1203,9 +1203,8 @@ static int load_elf_library(struct file *file)
 
 	eppnt = elf_phdata;
 	error = -ENOEXEC;
-	pos =  elf_ex.e_phoff;
-	retval = kernel_read(file, eppnt, j, &pos);
-	if (retval != j)
+	retval = elf_read(file, eppnt, j, elf_ex.e_phoff);
+	if (retval < 0)
 		goto out_free_ph;
 
 	for (j = 0, i = 0; i<elf_ex.e_phnum; i++)