Greg, Sasha,

Can you please backport this commit (below) to a stable 6.1.y tree, it's confirmed be Kees this could cause kernel panic due to false positive strncpy fortify, and this is already happened for some users.

Thanks,

On Fri, Feb 09, 2024 at 04:02:32PM -0800, Kees Cook wrote:

On Sat, Feb 10, 2024 at 01:13:06AM +0300, Vitaly Chikunov wrote:

...

On Tue, Feb 14, 2023 at 04:08:39PM -0800, Kees Cook wrote:

...

The kernel is globally removing the ambiguous 0-length and 1-element arrays in favor of flexible arrays, so that we can gain both compile-time and run-time array bounds checking[1].

While struct fealist is defined as a "fake" flexible array (via a 1-element array), it is only used for examination of the first array element. Walking the list is performed separately, so there is no reason to treat the "list" member of struct fealist as anything other than a single entry. Adjust the struct and code to match.

Additionally, struct fea uses the "name" member either as a dynamic string, or is manually calculated from the start of the struct. Redefine the member as a flexible array.

No machine code output differences are produced after these changes.

[1] For lots of details, see both: https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-... https://people.kernel.org/kees/bounded-flexible-arrays-in-c

Cc: Steve French sfrench@samba.org Cc: Paulo Alcantara pc@cjr.nz Cc: Ronnie Sahlberg lsahlber@redhat.com Cc: Shyam Prasad N sprasad@microsoft.com Cc: Tom Talpey tom@talpey.com Cc: linux-cifs@vger.kernel.org Cc: samba-technical@lists.samba.org Signed-off-by: Kees Cook keescook@chromium.org

---

fs/cifs/cifspdu.h | 4 ++-- fs/cifs/cifssmb.c | 16 ++++++++-------- 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/cifs/cifspdu.h b/fs/cifs/cifspdu.h index 623caece2b10..add73be4902c 100644 --- a/fs/cifs/cifspdu.h +++ b/fs/cifs/cifspdu.h @@ -2583,7 +2583,7 @@ struct fea { unsigned char EA_flags; __u8 name_len; __le16 value_len;

• char name[1];

• char name[]; /* optionally followed by value */

} __attribute__((packed)); /* flags for _FEA.fEA */ @@ -2591,7 +2591,7 @@ struct fea { struct fealist { __le32 list_len;

• struct fea list[1];

• struct fea list;

} __attribute__((packed)); /* used to hold an arbitrary blob of data */ diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c index 60dd4e37030a..7c587157d030 100644 --- a/fs/cifs/cifssmb.c +++ b/fs/cifs/cifssmb.c @@ -5787,7 +5787,7 @@ CIFSSMBQAllEAs(const unsigned int xid, struct cifs_tcon *tcon, /* account for ea list len */ list_len -= 4;

• temp_fea = ea_response_data->list;

• temp_fea = &ea_response_data->list; temp_ptr = (char *)temp_fea; while (list_len > 0) { unsigned int name_len;

@@ -5902,7 +5902,7 @@ CIFSSMBSetEA(const unsigned int xid, struct cifs_tcon *tcon, else name_len = strnlen(ea_name, 255);

• count = sizeof(*parm_data) + ea_value_len + name_len;

• count = sizeof(*parm_data) + 1 + ea_value_len + name_len; pSMB->MaxParameterCount = cpu_to_le16(2); /* BB find max SMB PDU from sess */ pSMB->MaxDataCount = cpu_to_le16(1000);

@@ -5926,14 +5926,14 @@ CIFSSMBSetEA(const unsigned int xid, struct cifs_tcon *tcon, byte_count = 3 /* pad */ + params + count; pSMB->DataCount = cpu_to_le16(count); parm_data->list_len = cpu_to_le32(count);

• parm_data->list[0].EA_flags = 0;

• parm_data->list.EA_flags = 0; /* we checked above that name len is less than 255 */

• parm_data->list[0].name_len = (__u8)name_len;

• parm_data->list.name_len = (__u8)name_len; /* EA names are always ASCII */ if (ea_name)

• strncpy(parm_data->list[0].name, ea_name, name_len);
  

• parm_data->list[0].name[name_len] = 0;
• parm_data->list[0].value_len = cpu_to_le16(ea_value_len);

• strncpy(parm_data->list.name, ea_name, name_len);
  

Could non-applying this patch cause false-positive fortify_panic? We got a bug report from user of 6.1.73:

Jan 24 15:15:20 kalt2test.dpt.local kernel: detected buffer overflow in strncpy

Yes, this seems likely. I would backport this change.

...

Jan 24 15:15:20 kalt2test.dpt.local kernel: ------------[ cut here ]------------ Jan 24 15:15:20 kalt2test.dpt.local kernel: kernel BUG at lib/string_helpers.c:1027! ... Jan 24 15:15:20 kalt2test.dpt.local kernel: Call Trace: Jan 24 15:15:20 kalt2test.dpt.local kernel: CIFSSMBSetEA.cold+0xc/0x18 [cifs] Jan 24 15:15:20 kalt2test.dpt.local kernel: cifs_xattr_set+0x596/0x690 [cifs] Jan 24 15:15:20 kalt2test.dpt.local kernel: __vfs_removexattr+0x52/0x70 Jan 24 15:15:20 kalt2test.dpt.local kernel: __vfs_removexattr_locked+0xbc/0x150 Jan 24 15:15:20 kalt2test.dpt.local kernel: vfs_removexattr+0x56/0x100 Jan 24 15:15:20 kalt2test.dpt.local kernel: removexattr+0x58/0x90 Jan 24 15:15:20 kalt2test.dpt.local kernel: __ia32_sys_fremovexattr+0x80/0xa0 Jan 24 15:15:20 kalt2test.dpt.local kernel: int80_emulation+0xa9/0x110 Jan 24 15:15:20 kalt2test.dpt.local kernel: asm_int80_emulation+0x16/0x20

This appears to be a compat call?

-Kees

...

I don't find this patch appled to stable/linux-6.1.y.

Thanks,

ps. (Unfortunately `CIFSSMBSetEA+0xc` address is not resolvable to the actual line inside of CIFSSMBSetEA pointing just to the head of it.

(gdb) l *CIFSSMBSetEA+0xc 0x6de3c is in CIFSSMBSetEA (fs/smb/client/cifssmb.c:5776). 5771 int 5772 CIFSSMBSetEA(const unsigned int xid, struct cifs_tcon *tcon, 5773 const char *fileName, const char *ea_name, const void *ea_value, 5774 const __u16 ea_value_len, const struct nls_table *nls_codepage, 5775 struct cifs_sb_info *cifs_sb) 5776 { 5777 struct smb_com_transaction2_spi_req *pSMB = NULL; 5778 struct smb_com_transaction2_spi_rsp *pSMBr = NULL; 5779 struct fealist *parm_data; 5780 int name_len;

But there is only one strncpy there.

...

• parm_data->list.name[name_len] = '\0';
• parm_data->list.value_len = cpu_to_le16(ea_value_len); /* caller ensures that ea_value_len is less than 64K but we need to ensure that it fits within the smb */

@@ -5941,7 +5941,7 @@ CIFSSMBSetEA(const unsigned int xid, struct cifs_tcon *tcon, negotiated SMB buffer size BB */ /* if (ea_value_len > buffer_size - 512 (enough for header)) */ if (ea_value_len)

• memcpy(parm_data->list[0].name+name_len+1,
  

• memcpy(parm_data->list.name + name_len + 1,
    ea_value, ea_value_len);
  

pSMB->TotalDataCount = pSMB->DataCount; -- 2.34.1

-- Kees Cook