[v2,3/6] elf: Fix failure handling in _dl_map_object_from_fd

Commit Message

Szabolcs Nagy Nov. 27, 2020, 1:20 p.m. UTC

There are many failure paths that call lose to do local cleanups
in _dl_map_object_from_fd, but it did not clean everything.

Handle l_phdr, l_libname and mapped segments in the common failure
handling code.

There are various bits that may not be cleaned properly on failure
(e.g. executable stack, tlsid, incomplete dl_map_segments).
---
 elf/dl-load.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

Comments

Adhemerval Zanella Netto Dec. 10, 2020, 6:25 p.m. UTC | #1

On 27/11/2020 10:20, Szabolcs Nagy via Libc-alpha wrote:
> There are many failure paths that call lose to do local cleanups
> in _dl_map_object_from_fd, but it did not clean everything.
> 
> Handle l_phdr, l_libname and mapped segments in the common failure
> handling code.
> 
> There are various bits that may not be cleaned properly on failure
> (e.g. executable stack, tlsid, incomplete dl_map_segments).
> ---
>  elf/dl-load.c | 24 +++++++++++++++---------
>  1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index 21e55deb19..9c71b7562c 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -914,8 +914,15 @@ lose (int code, int fd, const char *name, char *realname, struct link_map *l,
>    /* The file might already be closed.  */
>    if (fd != -1)
>      (void) __close_nocancel (fd);
> +  if (l != NULL && l->l_map_start != 0)
> +    _dl_unmap_segments (l);
>    if (l != NULL && l->l_origin != (char *) -1l)
>      free ((char *) l->l_origin);
> +  if (l != NULL && !l->l_libname->dont_free)
> +    free (l->l_libname);
> +  if (l != NULL && l->l_phdr_allocated)
> +    free ((void *) l->l_phdr);
> +
>    free (l);
>    free (realname);
>  
> @@ -1256,7 +1263,11 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
>      errstring = _dl_map_segments (l, fd, header, type, loadcmds, nloadcmds,
>  				  maplength, has_holes, loader);
>      if (__glibc_unlikely (errstring != NULL))
> -      goto call_lose;
> +      {
> +	/* Mappings can be in an inconsistent state: avoid unmap.  */
> +	l->l_map_start = l->l_map_end = 0;
> +	goto call_lose;
> +      }
>  
>      /* Process program headers again after load segments are mapped in
>         case processing requires accessing those segments.  Scan program

In this case I am failing to see who would be responsible to unmap 
l_map_start int the type == ET_DYN where first mmap succeeds but
with a later mmap failure in any load command.

> @@ -1294,14 +1305,6 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
>        || (__glibc_unlikely (l->l_flags_1 & DF_1_PIE)
>  	  && __glibc_unlikely ((mode & __RTLD_OPENEXEC) == 0)))
>      {
> -      /* We are not supposed to load this object.  Free all resources.  */
> -      _dl_unmap_segments (l);
> -
> -      if (!l->l_libname->dont_free)
> -	free (l->l_libname);
> -
> -      if (l->l_phdr_allocated)
> -	free ((void *) l->l_phdr);
>  
>        if (l->l_flags_1 & DF_1_PIE)
>  	errstring
> @@ -1392,6 +1395,9 @@ cannot enable executable stack as shared object requires");
>    /* Signal that we closed the file.  */
>    fd = -1;
>  
> +  /* Failures before this point are handled locally via lose.
> +     No more failures are allowed in this function until return.  */
> +
>    /* If this is ET_EXEC, we should have loaded it as lt_executable.  */
>    assert (type != ET_EXEC || l->l_type == lt_executable);
>  
> 

Ok.

Szabolcs Nagy Dec. 11, 2020, 9:32 a.m. UTC | #2

The 12/10/2020 15:25, Adhemerval Zanella wrote:
> On 27/11/2020 10:20, Szabolcs Nagy via Libc-alpha wrote:
> > There are many failure paths that call lose to do local cleanups
> > in _dl_map_object_from_fd, but it did not clean everything.
> > 
> > Handle l_phdr, l_libname and mapped segments in the common failure
> > handling code.
> > 
> > There are various bits that may not be cleaned properly on failure
> > (e.g. executable stack, tlsid, incomplete dl_map_segments).
> > ---
> >  elf/dl-load.c | 24 +++++++++++++++---------
> >  1 file changed, 15 insertions(+), 9 deletions(-)
> > 
> > diff --git a/elf/dl-load.c b/elf/dl-load.c
> > index 21e55deb19..9c71b7562c 100644
> > --- a/elf/dl-load.c
> > +++ b/elf/dl-load.c
> > @@ -914,8 +914,15 @@ lose (int code, int fd, const char *name, char *realname, struct link_map *l,
> >    /* The file might already be closed.  */
> >    if (fd != -1)
> >      (void) __close_nocancel (fd);
> > +  if (l != NULL && l->l_map_start != 0)
> > +    _dl_unmap_segments (l);
> >    if (l != NULL && l->l_origin != (char *) -1l)
> >      free ((char *) l->l_origin);
> > +  if (l != NULL && !l->l_libname->dont_free)
> > +    free (l->l_libname);
> > +  if (l != NULL && l->l_phdr_allocated)
> > +    free ((void *) l->l_phdr);
> > +
> >    free (l);
> >    free (realname);
> >  
> > @@ -1256,7 +1263,11 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
> >      errstring = _dl_map_segments (l, fd, header, type, loadcmds, nloadcmds,
> >  				  maplength, has_holes, loader);
> >      if (__glibc_unlikely (errstring != NULL))
> > -      goto call_lose;
> > +      {
> > +	/* Mappings can be in an inconsistent state: avoid unmap.  */
> > +	l->l_map_start = l->l_map_end = 0;
> > +	goto call_lose;
> > +      }
> >  
> >      /* Process program headers again after load segments are mapped in
> >         case processing requires accessing those segments.  Scan program
> 
> In this case I am failing to see who would be responsible to unmap 
> l_map_start int the type == ET_DYN where first mmap succeeds but
> with a later mmap failure in any load command.

failures are either cleaned up locally in this function
via lose or after a clean return via dlclose.

failures that are not cleaned up will leak resources.

_dl_map_segments failure is not cleaned up (the mappings
are in an unknown state). however after a successful
_dl_map_segments later failures can clean the mappings
and that's what i fixed here.

i did not try to fix transitive design bugs (such as
leaks in _dl_map_segments) that would require interface
change or local cleanups in those other functions.

> > @@ -1294,14 +1305,6 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
> >        || (__glibc_unlikely (l->l_flags_1 & DF_1_PIE)
> >  	  && __glibc_unlikely ((mode & __RTLD_OPENEXEC) == 0)))
> >      {
> > -      /* We are not supposed to load this object.  Free all resources.  */
> > -      _dl_unmap_segments (l);
> > -
> > -      if (!l->l_libname->dont_free)
> > -	free (l->l_libname);
> > -
> > -      if (l->l_phdr_allocated)
> > -	free ((void *) l->l_phdr);
> >  
> >        if (l->l_flags_1 & DF_1_PIE)
> >  	errstring
> > @@ -1392,6 +1395,9 @@ cannot enable executable stack as shared object requires");
> >    /* Signal that we closed the file.  */
> >    fd = -1;
> >  
> > +  /* Failures before this point are handled locally via lose.
> > +     No more failures are allowed in this function until return.  */
> > +
> >    /* If this is ET_EXEC, we should have loaded it as lt_executable.  */
> >    assert (type != ET_EXEC || l->l_type == lt_executable);
> >  
> > 
> 
> Ok.

Patch

diff --git a/elf/dl-load.c b/elf/dl-load.c
index 21e55deb19..9c71b7562c 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -914,8 +914,15 @@  lose (int code, int fd, const char *name, char *realname, struct link_map *l,
   /* The file might already be closed.  */
   if (fd != -1)
     (void) __close_nocancel (fd);
+  if (l != NULL && l->l_map_start != 0)
+    _dl_unmap_segments (l);
   if (l != NULL && l->l_origin != (char *) -1l)
     free ((char *) l->l_origin);
+  if (l != NULL && !l->l_libname->dont_free)
+    free (l->l_libname);
+  if (l != NULL && l->l_phdr_allocated)
+    free ((void *) l->l_phdr);
+
   free (l);
   free (realname);
 
@@ -1256,7 +1263,11 @@  _dl_map_object_from_fd (const char *name, const char *origname, int fd,
     errstring = _dl_map_segments (l, fd, header, type, loadcmds, nloadcmds,
 				  maplength, has_holes, loader);
     if (__glibc_unlikely (errstring != NULL))
-      goto call_lose;
+      {
+	/* Mappings can be in an inconsistent state: avoid unmap.  */
+	l->l_map_start = l->l_map_end = 0;
+	goto call_lose;
+      }
 
     /* Process program headers again after load segments are mapped in
        case processing requires accessing those segments.  Scan program
@@ -1294,14 +1305,6 @@  _dl_map_object_from_fd (const char *name, const char *origname, int fd,
       || (__glibc_unlikely (l->l_flags_1 & DF_1_PIE)
 	  && __glibc_unlikely ((mode & __RTLD_OPENEXEC) == 0)))
     {
-      /* We are not supposed to load this object.  Free all resources.  */
-      _dl_unmap_segments (l);
-
-      if (!l->l_libname->dont_free)
-	free (l->l_libname);
-
-      if (l->l_phdr_allocated)
-	free ((void *) l->l_phdr);
 
       if (l->l_flags_1 & DF_1_PIE)
 	errstring
@@ -1392,6 +1395,9 @@  cannot enable executable stack as shared object requires");
   /* Signal that we closed the file.  */
   fd = -1;
 
+  /* Failures before this point are handled locally via lose.
+     No more failures are allowed in this function until return.  */
+
   /* If this is ET_EXEC, we should have loaded it as lt_executable.  */
   assert (type != ET_EXEC || l->l_type == lt_executable);