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Message-ID: <1525639f-560f-2677-b1cb-f904b3552c71@linaro.org>
Date: Thu, 10 Dec 2020 15:25:12 -0300
From: Adhemerval Zanella <adhemerval.zanella@...aro.org>
To: Szabolcs Nagy <szabolcs.nagy@....com>, libc-alpha@...rceware.org
Cc: Mark Rutland <mark.rutland@....com>, kernel-hardening@...ts.openwall.com,
Catalin Marinas <catalin.marinas@....com>, linux-kernel@...r.kernel.org,
Jeremy Linton <jeremy.linton@....com>, Mark Brown <broonie@...nel.org>,
Topi Miettinen <toiwoton@...il.com>, Will Deacon <will@...nel.org>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 3/6] elf: Fix failure handling in
_dl_map_object_from_fd
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.
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