| Message ID | 20230925194040.68592-2-vsementsov@yandex-team.ru (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | coverity fixes | expand |
On Mon, 25 Sept 2023 at 20:41, Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> wrote: > > This @size parameter often comes from fd. We'd better check it before > doing read and allocation. > > Chose 1G as high enough empiric bound. Empirical for who? > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> > --- > hw/core/loader.c | 17 ++++++++++++++++- > 1 file changed, 16 insertions(+), 1 deletion(-) > > diff --git a/hw/core/loader.c b/hw/core/loader.c > index 4dd5a71fb7..4b67543046 100644 > --- a/hw/core/loader.c > +++ b/hw/core/loader.c > @@ -281,11 +281,26 @@ ssize_t load_aout(const char *filename, hwaddr addr, int max_sz, > > /* ELF loader */ > > +#define ELF_LOAD_MAX (1024 * 1024 * 1024) > + > static void *load_at(int fd, off_t offset, size_t size) > { > void *ptr; > - if (lseek(fd, offset, SEEK_SET) < 0) > + > + /* > + * We often come here with @size, which was previously read from file > + * descriptor too. That's not good to read and allocate for unchecked > + * number of bytes. Coverity also doesn't like it and generate problems. > + * So, let's limit all load_at() calls to ELF_LOAD_MAX at least. > + */ > + if (size > ELF_LOAD_MAX) { > return NULL; > + } > + > + if (lseek(fd, offset, SEEK_SET) < 0) { > + return NULL; > + } > + > ptr = g_malloc(size); > if (read(fd, ptr, size) != size) { > g_free(ptr); This doesn't really help anything: (1) if the value is really big, it doesn't cause any terrible consequences -- QEMU will just exit because the allocation fails, which is fine because this will be at QEMU startup and only happens if the user running QEMU gives us a silly file (2) we do a lot of other "allocate and abort on failure" elsewhere in the ELF loader, for instance the allocations of the symbol table and relocs in the load_symbols and elf_reloc functions, and then on a bigger scale when we work with the actual data in the ELF file thanks -- PMM
On 26.09.23 13:33, Peter Maydell wrote: > On Mon, 25 Sept 2023 at 20:41, Vladimir Sementsov-Ogievskiy > <vsementsov@yandex-team.ru> wrote: >> >> This @size parameter often comes from fd. We'd better check it before >> doing read and allocation. >> >> Chose 1G as high enough empiric bound. > > Empirical for who? > >> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> >> --- >> hw/core/loader.c | 17 ++++++++++++++++- >> 1 file changed, 16 insertions(+), 1 deletion(-) >> >> diff --git a/hw/core/loader.c b/hw/core/loader.c >> index 4dd5a71fb7..4b67543046 100644 >> --- a/hw/core/loader.c >> +++ b/hw/core/loader.c >> @@ -281,11 +281,26 @@ ssize_t load_aout(const char *filename, hwaddr addr, int max_sz, >> >> /* ELF loader */ >> >> +#define ELF_LOAD_MAX (1024 * 1024 * 1024) >> + >> static void *load_at(int fd, off_t offset, size_t size) >> { >> void *ptr; >> - if (lseek(fd, offset, SEEK_SET) < 0) >> + >> + /* >> + * We often come here with @size, which was previously read from file >> + * descriptor too. That's not good to read and allocate for unchecked >> + * number of bytes. Coverity also doesn't like it and generate problems. >> + * So, let's limit all load_at() calls to ELF_LOAD_MAX at least. >> + */ >> + if (size > ELF_LOAD_MAX) { >> return NULL; >> + } >> + >> + if (lseek(fd, offset, SEEK_SET) < 0) { >> + return NULL; >> + } >> + >> ptr = g_malloc(size); >> if (read(fd, ptr, size) != size) { >> g_free(ptr); > > This doesn't really help anything: > (1) if the value is really big, it doesn't cause any terrible > consequences -- QEMU will just exit because the allocation > fails, which is fine because this will be at QEMU startup > and only happens if the user running QEMU gives us a silly file > (2) we do a lot of other "allocate and abort on failure" > elsewhere in the ELF loader, for instance the allocations of > the symbol table and relocs in the load_symbols and > elf_reloc functions, and then on a bigger scale when we > work with the actual data in the ELF file Reasonable.. Don't you have an idea, how to somehow mark the value "trusted" for Coverity?
On Tue, 26 Sept 2023 at 11:51, Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> wrote: > > On 26.09.23 13:33, Peter Maydell wrote: > > On Mon, 25 Sept 2023 at 20:41, Vladimir Sementsov-Ogievskiy > > <vsementsov@yandex-team.ru> wrote: > >> > >> This @size parameter often comes from fd. We'd better check it before > >> doing read and allocation. > >> > >> Chose 1G as high enough empiric bound. > > > > Empirical for who? > > > >> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> > >> --- > >> hw/core/loader.c | 17 ++++++++++++++++- > >> 1 file changed, 16 insertions(+), 1 deletion(-) > >> > >> diff --git a/hw/core/loader.c b/hw/core/loader.c > >> index 4dd5a71fb7..4b67543046 100644 > >> --- a/hw/core/loader.c > >> +++ b/hw/core/loader.c > >> @@ -281,11 +281,26 @@ ssize_t load_aout(const char *filename, hwaddr addr, int max_sz, > >> > >> /* ELF loader */ > >> > >> +#define ELF_LOAD_MAX (1024 * 1024 * 1024) > >> + > >> static void *load_at(int fd, off_t offset, size_t size) > >> { > >> void *ptr; > >> - if (lseek(fd, offset, SEEK_SET) < 0) > >> + > >> + /* > >> + * We often come here with @size, which was previously read from file > >> + * descriptor too. That's not good to read and allocate for unchecked > >> + * number of bytes. Coverity also doesn't like it and generate problems. > >> + * So, let's limit all load_at() calls to ELF_LOAD_MAX at least. > >> + */ > >> + if (size > ELF_LOAD_MAX) { > >> return NULL; > >> + } > >> + > >> + if (lseek(fd, offset, SEEK_SET) < 0) { > >> + return NULL; > >> + } > >> + > >> ptr = g_malloc(size); > >> if (read(fd, ptr, size) != size) { > >> g_free(ptr); > > > > This doesn't really help anything: > > (1) if the value is really big, it doesn't cause any terrible > > consequences -- QEMU will just exit because the allocation > > fails, which is fine because this will be at QEMU startup > > and only happens if the user running QEMU gives us a silly file > > (2) we do a lot of other "allocate and abort on failure" > > elsewhere in the ELF loader, for instance the allocations of > > the symbol table and relocs in the load_symbols and > > elf_reloc functions, and then on a bigger scale when we > > work with the actual data in the ELF file > > Reasonable.. > > Don't you have an idea, how to somehow mark the value "trusted" for Coverity? In the web UI, I just mark it "false positive" in the dropdown, and move on. Coverity has an absolute ton of false positives, and you really can't work with it unless you have a workflow for ignoring them. thanks -- PMM
On 26.09.23 13:54, Peter Maydell wrote: > On Tue, 26 Sept 2023 at 11:51, Vladimir Sementsov-Ogievskiy > <vsementsov@yandex-team.ru> wrote: >> >> On 26.09.23 13:33, Peter Maydell wrote: >>> On Mon, 25 Sept 2023 at 20:41, Vladimir Sementsov-Ogievskiy >>> <vsementsov@yandex-team.ru> wrote: >>>> >>>> This @size parameter often comes from fd. We'd better check it before >>>> doing read and allocation. >>>> >>>> Chose 1G as high enough empiric bound. >>> >>> Empirical for who? >>> >>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> >>>> --- >>>> hw/core/loader.c | 17 ++++++++++++++++- >>>> 1 file changed, 16 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/hw/core/loader.c b/hw/core/loader.c >>>> index 4dd5a71fb7..4b67543046 100644 >>>> --- a/hw/core/loader.c >>>> +++ b/hw/core/loader.c >>>> @@ -281,11 +281,26 @@ ssize_t load_aout(const char *filename, hwaddr addr, int max_sz, >>>> >>>> /* ELF loader */ >>>> >>>> +#define ELF_LOAD_MAX (1024 * 1024 * 1024) >>>> + >>>> static void *load_at(int fd, off_t offset, size_t size) >>>> { >>>> void *ptr; >>>> - if (lseek(fd, offset, SEEK_SET) < 0) >>>> + >>>> + /* >>>> + * We often come here with @size, which was previously read from file >>>> + * descriptor too. That's not good to read and allocate for unchecked >>>> + * number of bytes. Coverity also doesn't like it and generate problems. >>>> + * So, let's limit all load_at() calls to ELF_LOAD_MAX at least. >>>> + */ >>>> + if (size > ELF_LOAD_MAX) { >>>> return NULL; >>>> + } >>>> + >>>> + if (lseek(fd, offset, SEEK_SET) < 0) { >>>> + return NULL; >>>> + } >>>> + >>>> ptr = g_malloc(size); >>>> if (read(fd, ptr, size) != size) { >>>> g_free(ptr); >>> >>> This doesn't really help anything: >>> (1) if the value is really big, it doesn't cause any terrible >>> consequences -- QEMU will just exit because the allocation >>> fails, which is fine because this will be at QEMU startup >>> and only happens if the user running QEMU gives us a silly file >>> (2) we do a lot of other "allocate and abort on failure" >>> elsewhere in the ELF loader, for instance the allocations of >>> the symbol table and relocs in the load_symbols and >>> elf_reloc functions, and then on a bigger scale when we >>> work with the actual data in the ELF file >> >> Reasonable.. >> >> Don't you have an idea, how to somehow mark the value "trusted" for Coverity? > > In the web UI, I just mark it "false positive" in the dropdown, and > move on. Coverity has an absolute ton of false positives, and you > really can't work with it unless you have a workflow for ignoring them. > Yes, I have the possibility to mark "false positives", but tried to fix some things in the code which seemed reasonable to me. Thanks a lot for reviewing and explaining!
diff --git a/hw/core/loader.c b/hw/core/loader.c index 4dd5a71fb7..4b67543046 100644 --- a/hw/core/loader.c +++ b/hw/core/loader.c @@ -281,11 +281,26 @@ ssize_t load_aout(const char *filename, hwaddr addr, int max_sz, /* ELF loader */ +#define ELF_LOAD_MAX (1024 * 1024 * 1024) + static void *load_at(int fd, off_t offset, size_t size) { void *ptr; - if (lseek(fd, offset, SEEK_SET) < 0) + + /* + * We often come here with @size, which was previously read from file + * descriptor too. That's not good to read and allocate for unchecked + * number of bytes. Coverity also doesn't like it and generate problems. + * So, let's limit all load_at() calls to ELF_LOAD_MAX at least. + */ + if (size > ELF_LOAD_MAX) { return NULL; + } + + if (lseek(fd, offset, SEEK_SET) < 0) { + return NULL; + } + ptr = g_malloc(size); if (read(fd, ptr, size) != size) { g_free(ptr);
This @size parameter often comes from fd. We'd better check it before doing read and allocation. Chose 1G as high enough empiric bound. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> --- hw/core/loader.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)